Diffusing film comprising transparent resin and scatterers

ABSTRACT

A diffusing film comprises a transparent resin in which scatterers are dispersed. The difference between the refractive index of the transparent resin and that of the scatterers is in the range of 0.04 to 1.5. The scatterers are flat particles having sizes of 0.1 to 50 μm.

FIELD OF THE INVENTION

[0001] The present invention relates to a diffusing film, which can beattached on z screen side in a liquid crystal display. In detail, theinvention relates to a diffusing film and a polarizing plate thatimprove quality of an image given by a liquid crystal display.

BACKGROUND OF THE INVENTION

[0002] A liquid crystal display generally comprises a polarizing plateand a liquid crystal cell. For ensuring the quality of displayed images,the viewing angle must be enlarged and the display surface (screen) mustbe prevented from reflecting light coming from outside.

[0003] The most widely used display is a TFT liquid crystal display ofTN mode, in which an optical compensatory sheet is provided between thepolarizing plate and the liquid crystal cell. As described in JapanesePatent Provisional Publication Nos. 7(1995)-191217, 8(1996)-50206 andEuropean Patent No. 0911656A2, the TFT liquid crystal display of TN modegives an image of high quality within a wide viewing angle range.However, gradation of an image displayed by the TFT liquid crystaldisplay-is often inverted when the screen is seen downward.

[0004] To solve the problem, various proposals have been given. Forexample, it has been proposed that a diffusing means (Japanese PatentNo. 2,822,983), an optical axis exchanger (Japanese Patent PublicationNo. 2001-33783) or an optical means for diffusing emitted light(Japanese Patent Publication No. 2001-56461) be provided on the observerside surface to improve the image quality remarkably. However, in thesemethods, it is necessary to use a diffusing means having highlycontrolled lens or diffraction grating structure, which costs a lot andis very difficult to mass-produce.

[0005] Japanese Patent Provisional Publication Nos. 6(1994)-18706 and10(1998)-20103 disclose a diffusing film in which a transparentsubstrate is coated with a resin containing filler (e.g., siliconedioxide (silica)). That diffusing film can be mass-produced at low cost.

[0006] Japanese Patent Provisional Publication Nos. 11(1999)-160505,11(1999)-305010, 11(1999)-326608, 2000-121809, 2000-180611 and2000-338310 disclose other diffusing films, but they cannot fullyimprove the image quality.

[0007] Recently, liquid crystal displays have been often used asmonitors having enough fine pixels to display minute images. However,the monitors equipped with the diffusing films often display blurredimages.

[0008] For preventing the display surface from reflecting light comingfrom outside, an anti-reflection film is generally provided. Theanti-reflection film is placed on the top surface of the display, andcauses optical interference to reduce reflectance so that the displayingscreen may be prevented from reflecting surrounding scenes and therebyso that the contrast of displayed image may not impaired. However, theanti-reflection film by no means solves the problem of viewing angle(inversion of gradation), and therefore it has been wanted to provide ananti-reflection film which prevents well the display surface fromreflecting light coming from outside and at the same time which solvesthe problem of viewing angle.

SUMMERY OF THE INVENTION

[0009] It is an object of the present invention to provide a diffusingfilm and an anti-reflection film for enlarging the viewing angle ofliquid crystal display, particularly for preventing the display surfacefrom reflecting surrounding scenes and for preventing inversion ofgradation when the display is seen downward. The aimed films enable aliquid crystal display to give a clear image even if the display is usedas the minutely displaying monitor.

[0010] It is another object of the invention to provide a polarizingplate that enlarges the viewing angle (particularly, viewing angle whenthe display is seen downward) without thickening the liquid crystaldisplay. The aimed polarizing plate has improved durability, andprevents the image quality from impairments (such as deterioration ofcontrast, inversion of gradation or inversion of black to white or whiteto black, and unfavorable fluctuation of hue), which are often observedaccording to the viewing angle. The invention also aims to provide aliquid crystal display equipped with that polarizing plate.

[0011] The objects of the invention are achieved by the diffusing films(1) to (12), the processes for preparation of a diffusing film (13) to(15), the polarizing plates (16) to (18) and the liquid crystal displays(19) and (20), described below.

[0012] (1) A diffusing film comprising a transparent resin in whichscatterers are dispersed, wherein the difference between the refractiveindex of the transparent resin and that of the scatterers is in therange of 0.04 to 1.5, and wherein scatterers are flat particles havingparticle sizes in the range of 0.1 to 50 μm.

[0013] (2) The diffusing film of (1), wherein the scatterers are tabularparticles.

[0014] (3) The diffusing film of (2), wherein the ratio of the averagesize of scatterers in a section parallel to the film plane to that in asection perpendicular to the film plane is 2 or more.

[0015] (4) The diffusing film of (1), wherein the scatterers arecolumnar or rod-like particles.

[0016] (5) The diffusing film of (4), wherein the ratio of the averagesize of scatterers in the section parallel to the film plane to that inthe section perpendicular to the film plane is 0.5 or less.

[0017] (6) The diffusing film of (1), wherein at least one surface ofthe diffusing film has a surface roughness of 0.05 to 0.18 μm.

[0018] (7) The diffusing film of (1), wherein the transparent resinfurther contains a matting agent in the form of fine particles, and thedifference between the refractive index of the transparent resin andthat of the matting agent is less than 0.04.

[0019] (8) The diffusing film of (1), wherein the transparent resinfurthermore contains superfine particles whose particle sizes are lessthan 0.1 μm.

[0020] (9) The diffusing film of (1), wherein a scattering layercomprising the transparent resin and the scatterers dispersed therein isprovided on a transparent substrate.

[0021] (10) The diffusing film of (9), wherein the scattering layer hasa thickness of 2.0 to 6.0 μm.

[0022] (11) The diffusing film of (9), wherein a low-refractive indexlayer is further provided on the scattering layer.

[0023] (12) The diffusing film of (11), wherein an incident ray cominginto the low-refractive index layer at the incident angle of 5° isreflected in an average mirror reflectance of 2.5% or less in thewavelength region of 450 to 650 nm.

[0024] (13) A process for preparation of a diffusing film comprising thesteps of: dissolving or dispersing a transparent resin and scattererswhose refractive index differs from that of the transparent resin by0.04 to 1.5, in a mixture of a solvent having a function of dissolving atransparent substrate and another solvent having a function of notdissolving the substrate, to prepare a coating solution; applying thesolution onto the transparent substrate; and drying the solution to forma scattering layer containing flat scatters which have particle size of0.1 to 50 μm.

[0025] (14) The process of (13), wherein the scattering layer has athickness of 2.0 to 6.0 μm, and the transparent resin soaks into a depthof 0.01 to 1.0 μm in the substrate.

[0026] (15) The process of (13), wherein the substrate is made ofcellulose acetate, and the solvent dissolving the substrate contains aketone.

[0027] (16) A polarizing plate comprising a pair of protective films anda polarizing membrane provided between them, wherein one of theprotective films is a diffusing film comprising a transparent resin inwhich scatterers are dispersed, wherein the difference between therefractive index of the transparent resin and that of the scatterers isin the range of 0.04 to 1.5, and wherein scatterers are flat particleshaving particle sizes in the range of 0.1 to 50 μm.

[0028] (17) The polarizing plate of (16), wherein an opticallyanisotrbpic layer comprising a liquid crystal compound is provided onthe other protective film.

[0029] (18) The polarizing plate of (17), wherein the liquid crystalcompound is a discotic compound.

[0030] (19) A liquid crystal display of transmission type comprising apair of polarizing plates and a liquid crystal cell provided betweenthem, wherein the polarizing plate comprises a pair of protective filmsand a polarizing membrane provided between them, and the protective filmon the screen side is a diffusing film comprising a transparent resin inwhich scatterers are dispersed, wherein the difference between therefractive index of the transparent resin and that of the scatterers isin the range of 0.04 to 1.5, and wherein scatterers are flat particleshaving particle sizes in the range of 0.1 to 50 μm.

[0031] (20) A liquid crystal display of reflection type comprising areflection board, a liquid crystal cell and a polarizing plate in thisorder, wherein the polarizing plate comprises a pair of protective filmsand a polarizing membrane provided between them, and the protective filmon the screen side is a diffusing film comprising a transparent resin inwhich scatterers are dispersed, wherein the difference between therefractive index of the transparent resin and that of the scatterers isin the range of 0.04 to 1.5, and wherein scatterers are flat particleshaving particle sizes in the range of 0.1 to 50 μm.

[0032] The applicant has found that the scattering profile (intensityaccording to viewing angle) of light having passed through thescattering layer within a particular angle to the normal and the hazevalue thereof (particularly, the internal scattering haze value thereof,which greatly contributes to diffusion of the transmitted light) relateto improvement of the viewing angle character and to blur of thedisplayed image. In detail, according to the applicant's study, theintensity of light scattered within the angle of 40° to the normalenlarges the viewing angle, and that at an angle of 50° or more makesthe blur worse.

[0033] The applicant has further studied, and finally succeeded incontrolling the surface roughness by properly selecting shapes(sectional sizes seen at the observing angle) of the scatterers. Thesurface roughness is controlled so that the desired scattering profilecan be obtained. Further, a low-refractive index layer is formed on asurface having the properly controlled roughness to prepare ananti-reflection film, which can prevent the displaying screen fromreflecting surrounding scenes and also which can improve the viewingangle character without blurring the displayed image (consequently, thetransmitted image can be kept very clear).

[0034] Light emitted from the backlight is scattered by the diffusingfilm provided on the polarizing plate of the observer side. The more thelight is scattered within the angle of 40° to the normal, the more theviewing angle character is improved. However, if too much amount oflight is scattered at the angle of 50° or more to the normal, the blurbecomes worse. Further, if the light scattered at the angle of 90° ormore to the normal (light scattered backward) increases, the brightnessof image seen frontally is lowered or the clearness of image isimpaired.

[0035] Although conventional spherical scatterers can improve theviewing angle character, they at the same time make the blur worse orimpair the brightness of image seen frontally. In contrast, according tothe invention, the viewing angle character can be improved withoutimpairing the quality of displayed image (without lowering thebrightness and without causing the blur).

BRIEF DESCRIPTION OF THE DRAWING

[0036]FIG. 1 is a sectional view schematically illustrating an exampleof the anti-reflection film.

DETAILED DESCRIPTION OF THE INVENTION

[0037] [Basic Structure of Diffusing Film]

[0038] The diffusing film of the invention has a haze measured along thenormal preferably in the range of 1 to 40%, more preferably in the rangeof 5 to 30%, most preferably in the range of 7 to 20%.

[0039] The haze measured in the direction inclined from the normal ispreferably larger than that measured along the normal. For example, thehaze measured in the direction inclined at the angle of 30° to thenormal is preferably in the range of 20 to 70%, more preferably in therange of 30 to 60%.

[0040] In order to control the haze, the content of the scatterers maybe increased or the difference between the refractive index of thetransparent resin (binder) and that of the scatterers may be properlycontrolled.

[0041] In consideration of recognizability, it is also necessary to makethe film surface rough enough to give an adequate surface haze. Thefrontally measured haze (total of the internal scattering haze and thesurface haze when seen frontally) is preferably 10% or more.

[0042] The surface roughness also contributes to the blur of image. Thesurface roughness Ra is preferably 0.18 μm or less, more preferably 0.16μm or less, most preferably 0.14 μm or less. In order to obtain theproper surface haze described above, the surface roughness Ra ispreferably 0.05 μm or more.

[0043] The content of binder in the scattering layer is controlled sothat the layer may have a desired surface roughness. If the content ofbinder is too large, the particles hardly project on the surface of thelayer to lower the surface roughness. The content of binder can beincreased by increasing the amount of binder in a coating solution forforming the scattering layer, by controlling the solvent composition inthe coating solution, or by controlling conditions for drying theapplied solution in forming the layer. In order to obtain a smallsurface roughness, the applied solution is preferably dried so slowlythat the solution can fully level out to form a smooth surface. Further,to produce a smooth surface, it is also preferred that the solventcomposition hardly soak into (hardly dissolve) the transparentsubstrate. However, in consideration of adhesion between the scatteringlayer and the transparent substrate, it is necessary for the mixture ofsolvent composition to contain a solvent that soaks into (dissolves) thesubstrate at a certain degree.

[0044] The coating solution is treated at a temperature of 20 to 40° C.The solvent composition preferably comprises a solvent that dissolvesthe substrate (A) and another solvent that does not dissolve thesubstrate (B). As the former solvent (A), methyl ethyl ketone (whichdries relatively fast) is preferred. As the latter solvent (B), methylisobutyl ketone (which is also a kind of ketones) is preferred. Thetotal weight ratio of (A/B) is preferably in the range of 10/90 to30/70, more preferably in the range of 15/85 to 25/75.

[0045] A preferred embodiment of the anti-reflection film comprises atransparent support made of triacetyl cellulose, at least one scatteringlayer provided thereon, and at least one low refractive index layerfurther provided thereon.

[0046]FIG. 1 is a sectional view schematically illustrating an exampleof the anti-reflection film.

[0047] The anti-reflection film (1) comprises a transparent support madeof triacetyl cellulose (2), a scattering layer (3), and a low-refractiveindex layer (4), piled up in this order. In the scattering layer (3),scatterers (5) and matting particles (6) for controlling the surfaceroughness are dispersed. The scattering layer (3) may consist of two ormore sub-layers.

[0048] The transparent resin (binder) in the scattering layer has arefractive index preferably in the range of 1.50 to 2.00. The lowrefractive index layer has a refractive index preferably in the range of1.35 to 1.45. The refractive index of triacetyl cellulose (which is apreferred material for the transparent support) is 1.48.

[0049] Since the scattering layer (binder) has the above high refractiveindex, excellent anti-reflection effect can be obtained even if the lowrefractive index layer has a refractive index of 1.35 to 1.45.Accordingly, if the refractive index of the scattering layer is toosmall, the anti-reflection effect is impaired. On the other hand, if itis too large, the reflected light is undesirably colored.

[0050] [Scattering Layer]

[0051] The scattering layer preferably comprises scatterers, mattingparticles, and a transparent resin. As described above, the haze valueof an image frontally or obliquely seen is controlled with thescattering layer.

[0052] The scatterers used in the invention have the followingcharacters of (a) to (c):

[0053] (a) being flat,

[0054] (b) having a refractive index different from the refractive indexof the transparent resin by 0.04 to 1.5, and

[0055] (c) having particle sizes in the range of 0.1 to 50 μm.

[0056] In the above, the term “particle size” means the average oflengths parallel to the normal (Z) and parallel to the film surface (X,Y).

[0057] Further, the scatterers preferably have the following charactersof (d) and (e):

[0058] (d) having an average size of 0.1 to 50.0 μm in the sectionparallel to the film plane, and

[0059] (e) having an average size of 0.01 to 10.0 μm in the sectionperpendicular to the film plane.

[0060] The scattering intensity preferably varies continuously when theviewing angle is continuously changed to inline from the normal of thefilm, and therefore the flat scatterers are preferably columnar,rod-like or ellipsoidal (particularly, discotic) particles.

[0061] In the case where the scatterers are ellipsoidal particles, thelong axes of the particles are preferably almost perpendicular to thenormal. However, to enlarge the viewing angle in a particular direction,the particles may be aligned at a certain angle to the normal. In thatcase, the average aspect ratio is preferably 3 or more, more preferably5 or more, so that the film may work effectively in a liquid crystaldisplay (so that the viewing angle may be effectively enlarged withoutimpairing the contrast of image seen frontally and without blurring theimage). Further, in some cases, the scatterers having different aspectratios are mixed to use so that the viewing angle may be effectivelyenlarged.

[0062] The term “aspect ratio” here means the ratio of the scatterersize in the section parallel to the film surface per that perpendicularto the film surface (in the section including the normal of the film).

[0063] In the case where the scatterers are columnar or rod-likeparticles, the long axes of the particles are preferably almost parallelto the normal. The average aspect ratio is preferably 0.5 or less, morepreferably 0.3 or less, most preferably 0.2 or less.

[0064] The difference of the refractive index of the scatterers and thatof the transparent resin (binder) structuring the whole scattering layeris in the range of 0.04 to 1.5, preferably in the range of 0.04 to 1.0,more preferably in the range of 0.04 to 0.5, most preferably in therange of 0.04 to 0.2. If the difference is less than 0.04, it is toosmall to scatter light. If it is more than 1.5, the whole film whitens.

[0065] The scatterers have particle sizes in the range of 0.1 to 50 μm.

[0066] The matting particles are preferably transparent. Since thematting particles are used to control the surface roughness of thescattering layer, the difference between the refractive index of thematting particles and that of the binder is preferably small. Thedifference is preferably smaller than 0.04, more preferably smaller than0.03, most preferably 0.02 or less.

[0067] The sizes of the matting particles are preferably in the range of2.5 to 5.0 μm. They are properly controlled to realize the desiredsurface scattering.

[0068] In order to improve the quality of displayed image (to improvethe viewing angle when the screen is seen downward), it is necessary toscatter incident light obliquely coming into the scattering layer. Themore the light is scattered, the more the viewing angel character isimproved. However, to ensure the brightness of image seen frontally, itis preferred to scatter incident light vertically coming into thescattering layer as little as possible.

[0069] Further, in order to obtain the required image quality, it isalso necessary to prevent the screen from reflecting surrounding scenes.The smaller the surface haze value is, the less blurry and hence theclearer image the display gives. However, if the haze value is toosmall, the displaying screen is liable to reflect surrounding scenes andsparkles (scintillations) are often observed on the screen. In contrast,if it is too large, the displayed image is whitened (whitening; declineof black tone). Accordingly, the surface haze value (hs) satisfies thecondition of preferably 0.5<hs<30, more preferably 3≦hs≦20, mostpreferably 7≦hs≦15.

[0070] For controlling the surface haze value, fine particles areincorporated in the layer to make the surface adequately rough. The hazevalue can be determined by means of a measuring apparatus (HR-100,Murakami Shikisai Gijutsu-kenkyujo Co., Ltd,) according to JIS-K-7105.

[0071] If the mean particle size of the fine particles is 2.5 μm orless, the surface roughness is so little that incident light is notenough scattered to prevent the surface from reflecting surroundingscenes. If it is 5.0 μm or more, although the surface is rough enough tobe prevented from reflecting surrounding scenes, the surface isremarkably whitened to impair the image quality. Accordingly, the meanparticle size is preferably in the range of 2.2 to 4.7 μm, morepreferably in the range of 2.4 to 4.5 μm. The surface roughness (Ra) ispreferably 1.2 μm or less, more preferably 0.8 μm or less, mostpreferably 0.5 μm or less.

[0072] The scatterers and the matting particles may be mono-dispersedorganic or inorganic particles. The sizes of the particles arepreferably uniform. If so, the scattering characters of the particlesare almost the same, and hence the haze is easily controlled. Thematerial for the scatterers is not particularly restricted as long asits refractive index satisfies the above condition with that of thebinder.

[0073] For forming the scattering layer, organic or inorganic particlesare preferably dispersed as the flat scatterers in the transparentresin, and the dispersion is applied on a transparent substrate. Thescatterers can be prepared from various materials (e.g., proteins,silicon oxide, metal oxides, polymers). If the material is a polymer,the scatterers can be prepared by emulsion polymerization of monomer(for example, ester of polyhydric alcohols and (meth)acrylic acid) inthe stage of producing the diffusing film. The scatterers are preferablyfine particles of gelatin (refractive index: 1.44) or dipentaerythritolhexaacrylate polymer (refractive index: 1.51).

[0074] Further, commercially available fine particles may be used as thescatterers. Examples of the commercially available fine particlesinclude mica particles (Micromica, Coop Chemicals Co., Ltd.), silkprotein particles (Idemistu silk powder, Idemitsu PetrochemicalIndustries, Ltd.), and alumina particles (Ceraf, Yoshida Kogyo K.K.). Inaddition, as the columnar scatterers, fine columnar stacks of bariumferrite can be used.

[0075] The scattering layer containing the flat scatterers can be alsoformed by the steps of: dispersing and emulsifying the scatterers in thebinder to prepare a coating emulsion, applying the emulsion onto thetransparent substrate, and drying to let the layer shrink in thethickness direction (emulsification method). Otherwise, a coating liquidcontaining the binder and the scatterers having an aspect ratio of 2 ormore (discotic scatterers) dispersed therein may be applied on thesubstrate to form the scattering layer (dispersing method).

[0076] As the matting particles, plastic beads are preferred. Theplastic beads are preferably made of material having high transparency,and the difference between the refractive index of the material and thatof the transparent resin is preferably in the aforementioned range.

[0077] Examples of the material for the beads includepolymethylmethacrylate (refractive index: 1.51), acrylstyrene copolymer(refractive index: 1.55), melamine (refractive index: 1.57),polycarbonate (refractive index: 1.57), polystyrene (refractive index:1.60), crosslinked polystyrene (refractive index: 1.61), polyvinylchloride (refractive index: 1.60), and benzoguanamine-melamineformaldehyde (refractive index: 1.68).

[0078] The size of the plastic beads is preferably in the range of 0.5to 5 μm, as described above. The amount of the beads is preferably inthe range of 5 to 30 weight parts per 100 weight parts of thetransparent resin.

[0079] As the transparent resin, a composition comprising a commerciallyavailable polymer or a resin hardened with ultraviolet ray or electronbeam is used. An ionization radiation (i.e., ultraviolet ray or electronbeam)-setting resin, a mixture of ionization radiation-setting-resin andthermoplastic resin in a solvent, or a thermosetting resin can be used.

[0080] In the transparent resin, inorganic filler such as silica orzirconia may be added for preventing the transparent particles(scatterers and matting agent) from settling down or for controlling therefractive index. The more the inorganic filler is added, the more theparticles are prevented from settling down. However, if it is too muchadded, the transparency of the film is impaired. Accordingly, theinorganic filler consisting of grains having sizes of 0.5 μm or less arepreferably added in an amount of less than 0.1 wt. % based on the amountof the transparent resin. That amount of the filler hardly lowers thetransparency.

[0081] The thickness of the scattering layer is normally in the range of2 to 6 μm, preferably in the range of 3 to 5 μm.

[0082] The transparent resin has a refractive index preferably in therange of 1.50 to 2.00, more preferably in the range of 1.53 to 1.95,further preferably in the range of 1.57 to 1.90, most preferably in therange of 1.64 to 1.80. The refractive index of the transparent resin isdetermined by measuring the layer formed without the transparent fineparticles. If the refractive index is too small, the layer cannotprevent reflection well. On the other hand, if it is too high, thereflected light is unfavorably colored.

[0083] The transparent resin comprises a binder. The binder ispreferably a polymer having a main chain of saturated hydrocarbon orpolyether (more preferably, hydrocarbon), and the polymer is preferablycrosslinked. The polymer having a main chain of saturated hydrocarbon ispreferably prepared from ethylenically unsaturated monomers throughpolymerization reaction. The monomer preferably has two or moreethylenically unsaturated groups to form a crosslinked polymer.

[0084] Examples of the monomer having two or more ethylenicallyunsaturated polymerizable groups include esters of polyhydric alcoholand (meth)acrylic acid (e.g., ethylene glycol di(meth)acrylate,1,4-dichlorohexane diacrylate, pentaerythritol tetra(meth)acrylate,pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate,trimethylolethane tri(meth)acrylate, dipentaerythritoltetra(meth)acrylate, dipentaerythritol penta(meth)acrylate,dipentaerythritol hexa(meth)acrylate, 1,3,5-cyclohexanetrioltrimethacrylate, polyurethane polyacrylate, polyester polyacrylate),vinylbenzene and derivatives thereof (e.g., 1,4-divinylbenzene,4-vinylbenzoic acid-2-acryloyl ethylester, 1,4-divinylcyclohexanone),vinylsulfones (e.g., divinylsulfone), acrylamides (e.g., methylenebisacrylamide) and methacrylamide. In consideration of hardness andscratching resistance of the film, (meth)acrylate having three or morefunctional groups is preferred, and acrylate having five or morefunctional groups is more preferred. A mixture of dipentaerythritolpentaacrylate and dipentaerythritol hexaacrylate is commerciallyavailable and particularly preferably used.

[0085] These monomers having ethylenically unsaturated polymerizablegroups are dissolved in a solvent together with various polymerizationinitiators and additives. The thus-prepared solution (coating solution)is applied on a support, dried and polymerized to harden by ionizationradiation or heat.

[0086] In place of or in addition to the monomers having two or moreethylenically unsaturated polymerizable groups, crosslinking groups maybe introduced into the binder to be crosslinked. Examples of thecrosslinking group include isocyanate group, epoxy group, aziridinegroup, oxazolidine group, aldehyde group, carbonyl group, hydrazinegroup, carboxyl group, methylol group, and active methylene group.Further, the crosslinked structure can be obtained by the monomers suchas vinylsulfonic acid, acid anhydride, cyanoacrylate derivative,melamine, etherized methylol, ester, urethane, and methal alkoxide(e.g., tetramethoxy-silane). Furthermore, the binder may be crosslinkedby decomposition of some monomers such as block isocyanate group. As thecrosslinking group, not only groups that immediately induce crosslinkingreaction but also groups that are decomposed to cause the reaction canbe used. The binder having the crosslinking group can be crosslinked byheating.

[0087] Besides the above binder polymer, the transparent resin comprisesa copolymer of monomers having high refractive indexes and/or superfineparticles of metal oxide having a high refractive index.

[0088] Examples of the monomers having high refractive indexes includebis(4-methacryloylthiophenyl)sulfide, vinylnaphthalene,vinylphenylsulfide, and 4-methacryloxyphenyl-4′-methoxyphenylthioether.

[0089] The metal oxide having a high refractive index is preferably anoxide of at least one metal selected from the group consisting ofzirconium, titanium, aluminum, indium, zinc, tin and antimony. The sizeof the superfine particles is 100 nm or less, preferably 50 nm or less.The metal oxide is preferably an oxide of at least one metal selectedfrom the group consisting of Zr, Zn, Ti, In and Sn. Examples of themetal oxide include ZrO₂, TiO₂, Al₂O₃, In₂O₃, ZnO, SnO₂, Sb₂O₃ and ITO.Among then, ZrO₂ is particularly preferred. The amount of the monomershaving high refractive indexes or the superfine particles of metal oxideis in the range of 10 to 90 wt. %, preferably in the range of 20 to 80wt. % based on the total weight of the transparent resin.

[0090] The scattering layer containing the transparent resin is providedon the transparent substrate. For forming the layer, a solution of theresin is applied on the film. As a solvent of the solution, at least onesolvent dissolving material of the substrate (e.g., triacetyl cellulose)and at least one solvent not dissolving the material of the substrateare used in combination. That mixed solvent prevents the layer fromglaring, and at the same time enhances the adhesion between the layerand the substrate. Preferably, at least one solvent not dissolving thesubstrate has a higher boiling point than at least one solventdissolving the substrate. The highest boiling point of the solvents notdissolving the substrate is higher than the lowest boiling point of thesolvents dissolving the substrate more preferably by 30° C. or more,most preferably by 50° C. or more.

[0091] Examples of the solvent dissolving the material of the substrate(preferably, triacetyl cellulose) include ethers having 3 to 12 carbonatoms (e.g., dibutyl ether, dimethoxy methane, dimethoxy ethane,diethoxy ethane, propylene oxide, 1,4-dioxane, 1,3-dioxolane,1,3,5-trioxane, teterahydrofuran, anisole, phenetole), ketones having 3to 12 carbon atoms (e.g., acetone, methyl ethyl ketone, diethyl ketone,dipropyl ketone, diisobutyl ketone, cyclopentanone, cyclohexanone,methyl cyclohexanone), esters having 3 to 12 carbon atoms (e.g., ethylformate, propyl formate, n-pentyl formate, methyl acetate, ethylacetate, methyl propionate, ethyl propionate, n-pentyl acetate,y-butyrolactone), organic solvents having two or more kinds offunctional groups (e.g., methyl 2-methoxyacetate, methyl2-ethoxyacetate, ethyl 2-ethoxyacetate, ethyl 2-ethoxypropionate,2-methoxyehanol, 2-propoxyethanol, 2-butoxyethanol,1,2-diacetoxyacetone, acetylacetone, diacetonealcohol, methylacetoacetate, ethyl acetoacetate). These may be used singly or incombination. Ketones are preferred.

[0092] Examples of the solvent not dissolving the material of thesubstrate (preferably, triacetyl cellulose) include methanol, ethanol,1-propanol, 2-propanol, 1-butanol, 2-butanol, tert-butanol, 1-pentanol,2-methyl-2-butanol, cyclohexanol, isobutyl acetate, methyl isobutylketone, 2-octanone, 2-pentanone, 2-hexanone, 2-heptanone, 3-pentanone,3-heptanone and 4-heptanone. These may be used singly or in combination.

[0093] The ratio (A/B) of the total amount of the solvents dissolvingmaterial of the substrate (A) per the total amount of the solvents notdissolving that material (B) is preferably in the range of 5/95 to50/50, more preferably in the range of 10/90 to 40/60, most preferablyin the range of 15/85 to 30/70.

[0094] The aforementioned composition of ionization radiation-settingresin can be hardened in the normal manner, namely, by irradiation ofelectron beams or ultraviolet rays.

[0095] In the irradiation of electron beams, various electronaccelerators such as Cockcroft-Walton accelerator, Van de Graaffaccelerator, resonant transforming accelerator, insulatingcore-transforming accelerator, linear accelerator, dinamitron, andradio-frequency accelerator can be used. The electron beams have energyin the range of 50 to 1,000 KeV, preferably in the range of 100 to 300KeV. In the irradiation of ultraviolet rays, various light sources suchas extra high pressure mercury lamp, high pressure mercury lamp, lowpressure mercury lamp, carbon arc lamp, xenon arc lamp, and metal halidearc lamp can be used.

[0096] [Low Refractive Index Layer]

[0097] A low refractive index layer as an anti-reflection layer isprovided on the top surface of the scattering layer side, to prevent thefilm from reflecting light coming from outside.

[0098] The low refractive index layer has a refractive index in therange of 1.35 to 1.45.

[0099] The refractive index of the low refractive index layer preferablysatisfies the following formula (I):

(mλ/4)×0.7<n ₁ ×d ₁<(mλ/4)×1.3  Formula (I)

[0100] in which m is a positive odd number (usually 1), n₁ is therefractive index of the low refractive index layer, d₁ is the thickness(nm) of the low refractive index layer, and λ is a wavelength of visiblelight in the region of 450 to 650 nm.

[0101] When the refractive index (n₁) satisfies the formula (I), acertain positive odd number (m) (which is usually 1) satisfying theformula (I) can be found in the above wavelength region.

[0102] The low refractive index layer can be made of afluorine-containing resin prepared by hardening a thermosetting orionization radiation-setting crosslinkable fluorine-containing compound.The thus-prepared layer has better scratch resistance than a lowrefractive index layer made of magnesium fluoride or calcium fluoride.The hardened fluorine-containing resin has a refractive index in therange of 1.35 to 1.45. The hardened fluorine-containing resin has acoefficient of kinetic friction preferably in the range of 0.03 to 0.15,and gives a contact angle with water preferably in the range of 90° to120°.

[0103] Examples of the crosslinkable fluorine-containing compoundinclude a perfluoroalkyl-containing silane compound (e.g.,(heptadecafluoro-1,1,2,2-tetradecyl)triethoxysilane) and afluorine-containing copolymer derived from fluorine-containing monomersand monomers introducing crosslinking groups.

[0104] Examples of the fluorine-containing monomers includefluoroolefins (e.g., fluoroethylene, vinylidene fluoride,tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene,perfluoro-2,2-dimethyl-1,3-dioxole), partially or completely fluorinated(meth)acrylic alkyl ester derivatives (e.g., Biscoat 6FM [trade name,Osaka Organic Chemicals Co., Ltd.], M-2020 [trade name, Daikin Co.,Ltd.], and partially or completely fluorinated vinyl ethers.

[0105] Examples of the monomers introducing crosslinking groups includea (meth)acrylate monomer having a crosslinking group (e.g., glycidylmethacrylate), and a (meth)acrylate monomer having carboxyl, hydroxyl,amino or sulfonic acid group (e.g., (meth)acrylic acid, methylol(meth)acrylate, hydroxyalkyl (meth)acrylate, allylic acrylate). Afterthe (meth)acrylate monomers having carboxyl, hydroxyl, amino or sulfonicacid group are copolymerized, crosslinked structure can be formed in themanner described in Japanese Patent Provisional Publication Nos.10(1998)-25388 and 10(1998)-147739.

[0106] As well as the copolymer derived from fluorine-containingmonomers and monomers introducing crosslinking groups, a copolymerderived from these monomers and other monomers can be also used for thelow refractive index layer.

[0107] The usable monomers other than the above monomers are notparticularly restricted. Examples of them include olefins (e.g.,ethylene, propylene, isoprene, vinyl chloride, vinylidene chloride),acrylate esters (e.g., methyl acrylate, ethyl acrylate, 2-ethylhexylacrylate), methacrylate esters (e.g., methyl methacrylate, ethylmethacrylate, butyl methacrylate, ethylene glycol dimethacrylate),styrene derivatives (e.g., styrene, divinylbenzene, vinyltoluene,a-methylstyrene), vinyl ethers (e.g., methylvinyl ether), vinyl esters(e.g., vinyl acetate, vinyl propionate, vinyl cinnamate), acrylamides(e.g., N-tert-butylacrylamide, N-cyclohexylacrylamide), methacrylamidesand acrylonitrile derivatives.

[0108] In the fluorine-containing resin used in the low refractive indexlayer, superfine particles of Si oxide are preferably dispersed to makethe layer tough against scratching. The mean size of the Si oxideparticles is preferably 0.1 μm or less, more preferably in the range of0.001 to 0.05 μm. The lower refractive index the fluorine-containingresin has, the more the layer is prevented from reflecting light.However, if the refractive index is too low, the scratching resistanceis impaired. Accordingly, the refractive index of the resin and theamount of the Si oxide particles are controlled so adequately that therefractive index and the scratching resistance may be optimallybalanced.

[0109] As the superfine particles of Si oxide, commercially availablesilica sol dispersed in an organic solvent can be directly added to acoating solution for forming the low refractive index layer. Otherwise,various commercially available silica powders may be dispersed in anorganic solvent to prepare a silica dispersion to use.

[0110] When vertically peeled from a film of triacetyl cellulose (TAC)or polyethylene terephthalate (PET) at ordinary temperature and ordinaryhumidity, the anti-reflection film of the invention is electrifiedpreferably in the range of −200 to +200 pc (pico coulomb)/cm², morepreferably in the range of −100 to +100 pc/cm², further preferably inthe range of −50 to +50 pc/cm². Most preferably, the film is notelectrified. [The unit 1 pc means 10⁻¹² coulomb.]

[0111] In detail, the film is electrified at ordinary temperature and10%RH preferably in the range of −100 to +100 pc/cm², further preferablyin the range of −50 to +50 pc/cm². Most preferably, the film is notelectrified.

[0112] The above-described electrification degree (vertically-peelingelectrified charge) is measured in the following manner.

[0113] The sample to be measured is beforehand left for 2 hours or moreunder the condition of temperature and humidity for measurement. Themeasuring apparatus comprises a stage on which the sample is mounted, ahead which holds a testing film and which repeatedly compresses andpeels the testing film onto and from the sample, respectively, and anelectrometer which is provided on the head to measure electrified chargeon the sample. The sample is mounted on the stage, and then a TAC or PETtesting film is installed in the head. After the apparatus isdischarged, the head is repeatedly compressed onto and parted from thesample. The electrified charges after the testing film is peeled at thefirst and the fifth are measured and averaged. The procedure is repeatedwith respect to three samples, and the obtained values are averaged todetermine the vertically-peeling electrified charge.

[0114] It depends on the materials of the sample and the testing filmwhether the electrified charge is positive or negative. However, theabsolute value of the electrified charge is important.

[0115] Generally, a sample electrified at low humidity shows a highabsolute value of the electrified charge. In contrast, however, theanti-glaring anti-reflection film of the invention shows a low absolutevalue, even if electrified at low humidity.

[0116] The anti-reflection film of the invention shows a low absolutevalue of the electrified charge at ordinary temperature and ordinaryhumidity or 10%RH, and hence is excellent in dustproof.

[0117] The contents of various elements of the antireflection filmsurface are controlled so that the electrified charge may be in theabove-described range.

[0118] The anti-reflection film has a surface resistance of 1×10¹¹ Ω persquare or more, preferably 1×10¹² Ω per square or more. The surfaceresistance can be measured according to the disc electrode methodregulated in JIS. In the method, the current value is measured 1 minuteafter the voltage is applied so as to determine the surface resistance(SR).

[0119] It should be noted that the present invention essentially differsfrom a method in which the surface resistance is made small (forexample, 1×10¹⁰ Ω per square or less) enough to improve dustproof (toprevent the film from catching dust). Since the surface resistance istoo small to ensure the quality of displayed image, that method is notadopted in the invention. In the present invention, the absolute valueof the vertically-peeling electrified charge is made so small that thesurface resistance does not need to be small. Accordingly, the surfaceresistance in the invention can be set 1×10¹¹ Ω per square or more, andthereby the image quality is ensured.

[0120] The anti-reflection film reflects incident light of 450 to 650 nmcoming at the incident angle of 50 in an average mirror reflectance of2.5% or less. The average mirror reflectance is preferably 1.2% or less,more preferably 1.1% or less.

[0121] Further, the incident light of 450 to 650 nm coming at theincident angle of 5° is reflected preferably in an integratedreflectance of 2.5% or less. The average integrated reflectance is morepreferably 2.3% or less.

[0122] The light coming at the incident angle of 5° and the mirrorreflectance of that incident light are explained below.

[0123] The mirror reflectance of light coming at the incident angle of5° is a ratio of the intensity of light reflected out at the angle of−5° to the normal per the intensity of incident light coming at theangle of +50° to the normal. The mirror reflectance indicates how muchthe surface reflects surrounding scenes. The anti-glare anti-reflectionfilm shows a small mirror reflectance because it has a rough surface(which is provided for anti-glare performance) scattering the incidentlight to reduce the intensity of reflected light. Therefore, the mirrorreflectance indicates both anti-reflection character and anti-glarecharacter.

[0124] On the other hand, the integrated reflectance of light coming atthe incident angle of 5° is a ratio of the total intensity of lightreflected out in all directions per the intensity of incident lightcoming at the angle of +50° to the normal. Since it is not reduced byscattered light, the integrated reflectance indicates onlyanti-reflection character.

[0125] In the invention, the mirror reflectance and the integratedreflectance of light in the wavelength region of 450 to 650 nm coming atthe incident angle of 5° are both controlled at 2.5% or less to realizeboth satisfying anti-reflection character and sufficient anti-glarecharacter.

[0126] If the anti-reflection film reflects light in the wavelengthregion of 450 to 650 nm coming at the incident angle of 5° in an averagemirror reflectance of more than 2.5%, it mirrors surrounding scenes somuch that a display equipped with the film gives an image of poorrecognizability.

[0127] If the anti-reflection film reflects light in the wavelengthregion of 450 to 650 nm coming at the incident angle of 5° in an averageintegrated reflectance of more than 2.5%, a display equipped with thefilm gives an image of poor contrast. The displayed image is whitenedwith light scattered by the rough surface (which is provided foranti-glare performance), and accordingly the quality of the image isimpaired.

[0128] The anti-reflection film of the invention is preferably designedso that the incident light coming at the incident angle of 50° from theCIE standard light source D65 may be reflected to give ortho-reflectedlight having chromaticity satisfying the conditions of

[0129] L*≦10, 0≦a*≦2, and −5≦b*≦2

[0130] in which L*, a* and b* are values in L*a*b* color space of CIE1976. The reflected light having the above conditions shows neutralchromaticity.

[0131] The chromaticity of ortho-reflected light having been emittedfrom the CIE standard light source D65 and having entered at theincident angle of 5° can be evaluated in terms of the L*, a* and b*values in L*a*b* color space of CIE 1976. The L*, a* and b* values arecalculated from the spectral reflection spectrum, which is obtained fromthe product (at each wavelength) of the measured mirror reflectance oflight in the wavelength region of 380 to 780 nm coming at the incidentangle of 50° and the intensity (in the spectral distribution) oforiginal light emitted from the light source D65.

[0132] If the L* value is 10 or more, the film cannot fully prevent thedisplay surface from reflecting incident light. If the a* value is morethan 2, the reflected light is unnaturally colored in violet. On theother hand, if the a* value is less than 0, the reflected light isunnaturally colored greenly. If the b* value is less than −5, thereflected light is unnaturally colored in blue. On the other hand, ifthe b* value is more than 2, the reflected light is unnaturally coloredin yellow.

[0133] The refractive index of the low refractive index layer and thatof the binder material for the anti-glare layer are balanced optimallyso that the anti-reflection film may have a low refractive index and maygive reflected light having neutral chromaticity.

[0134] A known anti-reflection film comprising three or more opticalthin layers formed by deposition or spattering can be made to give anaverage mirror reflectance of 0.3% or less, and accordingly its L* valuecan be reduced to 3 or less. However, in that case, the a* and b* valuesare 10 or more and less than −10, respectively. Accordingly, the knownfilm gives unnaturally colored reflected light. In contrast, theanti-glare anti-reflection film of the invention is remarkably improvedin avoiding the unnatural coloring of reflected light.

[0135] [Transparent Substrate]

[0136] The transparent substrate is made of transparent resin ortransparent glass. Examples of the transparent resin include triacetylcellulose (TAC) (refractive index: 1.48), polyethylene terephthalate(PET), diacetylene cellulose, acetatebutylate cellulose, poly(ethersulphone), polyacrylic resin, polyurethane resin, polyester,polycarbonate, polysulfone, polyether, poly(methyl pentene), poly(etherketone), and (meth)acrylonitrile. The thickness of the substrate isnormally in the range of 25 to 1,000 μm.

[0137] The transparent substrate is provided on the top (or bottom)surface of the polarizing plate, and hence is preferably made ofcellulose acetate, which is generally used for a protective film of thepolarizing plate.

[0138] The substrate of cellulose acetate has both enough transparencyand enough smooth surfaces to be preferably used in the diffusing filmof the invention.

[0139] In the invention, cellulose acetate having an acetic acid contentof 59.0 to 61.5% is preferably used. The term “acetic acid content”means the amount of combined acetic acid per one unit weight ofcellulose. The acetic acid content is determined according to ASTM:D-817-91 (tests of cellulose acetate).

[0140] The cellulose ester has a viscosity average polymerization degree(DP) of preferably 250 or more, more preferably 290 or more. Further, itis also preferred for the cellulose ester used in the invention to havea narrow molecular weight distribution of Mw/Mn (Mw and Mn are weightand number average molecular weights, respectively), which is determinedby gel permeation chromatography. The value of Mw/Mn is preferably inthe range of 1.0 to 1.7, more preferably in the range of 1.3 to 1.65,most preferably in the range of 1.4 to 1.6.

[0141] Generally, hydroxyl groups at 2-, 3- and 6-position of celluloseacylate are not equally substituted (namely, the substitution degree ateach position is not equal to one third of the total substitutiondegree), and the substitution degree at 6-position is apt to berelatively small. In the cellulose acylate used in the invention, thesubstitution degree at 6-position is preferably larger than those at 2-and 3-positions.

[0142] The hydroxyl group at 6-position is substituted with acyl groupin an amount of preferably 32% or more, more preferably 33% or more,most preferably 34% or more, based on the total substitution degree.Further, the substitution degree of the acyl group at 6-position ispreferably 0.88 or more.

[0143] The hydroxyl group at 6-position may be substituted with acylgroup other than acetyl. Examples of the other acyl group are acylgroups having 3 or more carbon atoms (e.g., propionyl, butyloyl,valeroyl, benzoyl, acryloyl). The substitution degree at each positioncan be measured by means of NMR. Cellulose acylates prepared accordingto the methods described in Japanese Patent Provisional Publication No.11(1999)-5851 are usable for the invention.

[0144] [Preparation of Cellulose Acetate Film]

[0145] The cellulose acetate film is preferably prepared according tosolvent cast method. In the solvent cast method, a solution (dope) inwhich cellulose acetate is dissolved in an organic solvent is used.

[0146] Examples of the organic solvent include an ether having 3 to 12carbon atoms, a ketone having 3 to 12 carbon atoms, an ester having 3 to12 carbon atoms, and a halogenated hydrocarbon having 1 to 6 carbonatoms.

[0147] The ether, the ketone or the ester may have a cyclic structure. Acompound having two or more functional groups of ether, ketone or ester(—O—, —CO— or —COO—) is also usable as the solvent. The organic solventmay have other functional groups such as alcoholic hydroxyl. If thesolvent is the compound having two or more functional groups, the numberof carbon atoms is in any of the above ranges.

[0148] Examples of the ether having 3 to 12 carbon atoms includediisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane,1,3-dioxolan, tetrahydrofuran, anisole and phenetole.

[0149] Examples of the ketone having 3 to 12 carbon atoms includeacetone, methylethyl ketone, diethyl ketone, diisobutyl ketone,cyclohexanone and methylcyclohexane.

[0150] Examples of the ester having 3 to 12 carbon atoms include ethylformate, propyl formate, pentyl formate, methyl acetate, ethyl acetate,and pentyl acetate.

[0151] Examples of the compound having two or more functional groupsinclude 2-ethoxyethyl acetate, 2-methoxyethanol and 2-butoxyethanol.

[0152] The halogenated hydrocarbon. preferably has one or two carbonatoms, more preferably one carbon atom. The halogen is preferablychlorine. The hydrogen in the halogenated hydrocarbon is substitutedwith halogen in an amount of preferably 25 to 75 mol. %, more preferably30 to 70 mol. %, further preferably 35 to 65 mol. %, most preferably 40to 60 mol. %. A typical halogenated hydrocarbon is methylene chloride.

[0153] Two or more kinds of the solvents may be mixed to use incombination.

[0154] The cellulose acetate solution can be prepared in an ordinarymanner. The term “ordinary manner” means that the preparation is carriedout at a temperature of 0° C. or more (room temperature or elevatedtemperature). The cellulose acetate solution (dope) can be preparedthrough a common process by means of a common apparatus in the normalsolvent cast method. In the normal process, a halogenated hydrocarbon(particularly, methylene chloride) is preferably used as the solvent. Anon-chlorine-containing solvent is also usable as described in JapaneseTechnical Disclosure 2001-1745.

[0155] The amount of cellulose acetate in the solution is preferably inthe range of 10 to 40 wt. %, more preferably in the range of 10 to 30wt. %. To the organic (main) solvent, additives described after may beoptionally added.

[0156] Cellulose acetate and the organic solvent are mixed and stirredat room temperature (0 to 40° C.) to prepare the solution. For preparingthe concentrated solution, the preparation may be carried out at anelevated temperature under a high pressure. In that case, the celluloseacetate and the organic solvent are placed in a vessel resistingpressure. After the vessel is sealed, the mixture is stirred under anincreased pressure at an elevated temperature. The temperature iscontrolled so that it may be higher than the boiling point of thesolvent at atmospheric pressure but so that the solvent may not boil.The temperature is normally in the range of 40° C. or more, preferablyin the range of 60 to 200° C., more preferably in the range of 80 to110° C.

[0157] Before placed in the vessel, the components of the solution maybe beforehand mixed. They may be also added one by one into the vessel.The vessel must be equipped with a stirring means. Inactive gas such asnitrogen gas may be charged in the vessel to increase the innerpressure. Otherwise, the vessel may be heated to elevate the vaporpressure of the solvent so that the inner pressure may increase. Afterthe vessel is sealed, each component may be added under an elevatedpressure.

[0158] The vessel is preferably heated from outside. For example, ajacket heater is preferably used. Otherwise, liquid heated with a plateheater placed outside of the vessel may be made to flow through a pipewound around the vessel, to heat the whole vessel.

[0159] The mixture is preferably stirred with a propeller mixer providedin the vessel. The wing of the propeller preferably has a lengthreaching the inside wall of the vessel. Further, at the tip of the wing,a scratching mean is provided to scratch and renew liquid attached onthe inside wall.

[0160] In the vessel, various meters such as pressure gauge andthermometer may be provided. The components are dissolved in the solventin the vessel. The thus-prepared dope may be cooled and then taken outof the vessel, or may be taken out and then cooled with a heatexchanger.

[0161] The solution can be prepared according to the cooling dissolutionmethod, which makes it possible to dissolve cellulose acetate in anorganic solvent in which cellulose acetate cannot be dissolved by aconventional process. Further, according to that method, celluloseacetate can be rapidly and homogeneously dissolved in an organic solventin which cellulose acetate can. be dissolved by a conventional process.

[0162] First in the process of cooling dissolution method, celluloseacetate is gradually added with stirring into an organic solvent at roomtemperature.

[0163] The amount of cellulose acetate in the mixture is preferably inthe range of 10 to 40 wt. %, more preferably in the range of 10 to 30wt. %. Various additives described after may be added in the mixture.

[0164] The prepared mixture is cooled to a temperature of −100 to −10°C., preferably −80 to −10° C., more preferably −50 to −20° C., mostpreferably −50 to −30° C. The cooling procedure can be carried out, forexample, with dry ice-methanol bath (−75° C.) or with cooled ethyleneglycol solution (−30 to −20° C.). Through the cooling procedure, themixture is solidified.

[0165] The cooling rate is preferably 4° C./minute or more, morepreferably 8° C./minute or more, and most preferably 12° C./minute ormore. The cooling rate is preferably as fast as possible. However, atheoretical upper limit of the cooling rate is 10,000° C. per second, atechnical upper limit is 1,000° C. per second, and a practical upperlimit is 100° C. per second. The cooling rate means the change oftemperature at the cooling step per the time taken to complete thecooling step. The change of temperature means the difference between thetemperature at which the cooling step is started and the temperature atwhich the cooling step is completed.

[0166] The cooled mixture is then warmed to a temperature of 0 to 200°C., preferably 0 to 150° C., more preferably 0 to 120° C., mostpreferably 0 to 50° C. Through the warming procedure, cellulose acetateis dissolved in the organic solvent. For warming, the mixture may beleft at room temperature or may be heated in a warm bath.

[0167] The warming rate is 4° C./minute or more, more preferably 8°C./minute or more, and most preferably 12° C./minute or more. Thewarming rate is preferably as fast as possible. However, a theoreticalupper limit of the cooling rate is 10,000° C. per second, a technicalupper limit is 1,000° C. per second, and a practical upper limit is 100°C. per second. The warming rate means the change of temperature at thewarming step per the time taken to complete the warming step. The changeof temperature means the difference between the temperature at which thewarming step is started and the temperature at which the warming step iscompleted.

[0168] Thus, a homogeneous solution can be prepared. If celluloseacetate is not sufficiently dissolved, the cooling and warmingprocedures may be repeated. It can be judged by observation with theeyes whether cellulose acetate is sufficiently dissolved or not.

[0169] In the process of cooling dissolution method, a sealed vessel ispreferably used to prevent contamination of water, which may be causedby dew condensation at the cooling step. Further, the mixture may becooled under a reduced pressure so that the time taken to complete thecooling step can be shortened, and hence a vessel resisting pressure ispreferably used to conduct the procedures under a reduced pressure.

[0170] According to differential scanning calorimetric measurement(DSC), a 20 wt. % solution prepared by dissolving cellulose acetate(acetic acid content: 60.9%, viscosity average polymerization degree:299) in methyl acetate through the cooling dissolution process has apseudo-phase transition point between gel and sol at about 33° C. Belowthat temperature, the solution is in the form of homogeneous gel. Thesolution, therefore, must be kept at a temperature above thepseudo-phase transition point, preferably at a temperature higher thanthe pseudo-phase transition point by about 10° C. The pseudo-phasetransition point depends upon various conditions such as the organicsolvent, the acetic acid content, the viscosity average polymerizationdegree and the concentration of cellulose acetate.

[0171] The cellulose acetate film is formed from the prepared celluloseacetate solution (dope) according to the solvent cast method.

[0172] The dope is cast on a drum or a band, and the solvent isevaporated to form a film. The solid content of the dope is preferablycontrolled in the range of 18 to 35%. The surface of the drum or band ispreferably beforehand polished to be a mirror. The casting and dryingsteps of the casting method are described in U.S. Pat. Nos. 2,336,310,2,367,603, 2,492,078, 2,492,977, 2,492,978, 2,607,704, 2,739,069,2,739,070, British Patent Nos. 640,7-31, 736,892, Japanese PatentPublication Nos. 45(1970)-4554, 49(1974)-5614, Japanese PatentProvisional Publication Nos. 60(1985)-176834, 60(1985)-203430 and62(1987)-115035.

[0173] The surface temperature of the drum or band is preferably 10° C.or below. After cast on the drum or band, the dope is blown with air for2 seconds or more to dry. The formed film is then peeled, and blown withhot air whose temperature is successively changed from 100° C. to 160°C. in order to evaporate remaining solvent. This procedure is describedin Japanese Patent Publication No. 5(1993)-17844. That procedure canshorten the time taken to complete the steps of cooling to peeling. Forperforming the procedure, the cast dope must gel at the surfacetemperature of the drum or band.

[0174] From the prepared cellulose acylate solution (dope), a filmcomprising two or more layers can be formed. Also in that case, the filmis preferably formed by the solvent cast method. The dope is cast on adrum or a band, and the solvent is evaporated to form a film. The solidcontent of the dope is preferably controlled in the range of 10 to 40%.The surface of the drum or band is preferably beforehand polished to bea mirror.

[0175] Two or more cellulose acylate solutions can be cooperatively castto form two or more layers. For example, two or more outlets arearranged at intervals along the running direction of the support, andfrom each outlet each cellulose acylate solution is cast to form alayered film (Japanese Patent Provisional Publication Nos.61(1986)-158414, 1(1989)-122419 and 11(1999)-198285). Otherwise,cellulose acylate solutions may be cast from two outlets to form a film(Japanese Patent Publication No. 60(1985)-27562, Japanese PatentProvisional Publication Nos. 61(1986)-94724, 61(1986)-947245,61(1986)-104813, 61(1986)-158413 and 6(1994)-134933). Further, a flow ofhigh-viscous cellulose acylate solution may be enclosed with a flow oflow-viscous one to form a layered flow, and the high- and low-viscoussolutions in the layered flow may be simultaneously extruded to producea film (Japanese Patent Provisional Publication No. 56(1981)-162617).

[0176] Further, Japanese Patent Publication No. 44(1969)-20235 disclosesanother film preparation. In the disclosed process, a cellulose acylatesolution is cast on the support from one outlet to form a film. Afterpeeled from the support, the formed film is turned over and again placedon the support. On the thus appearing surface (having been in contactwith the support), another cellulose acylate solution is cast fromanother outlet to form a film.

[0177] The used cellulose acylate solutions may be the same or differentfrom each other. The function of each cellulose acylate layer can begiven by each corresponding solution extruded from each outlet.

[0178] Other functional layers (e.g., adhesive layer, dye layer,antistatic layer, anti-halation layer, UV absorbing layer, polarizinglayer) can be simultaneously formed from the cellulose acylate solutionsin the above manner.

[0179] In a conventional single layer preparation process, it isnecessary to extrude a cellulose acylate solution having such highconcentration and such high viscosity that the resultant film may havethe aimed thickness. Accordingly, that cellulose acylate solution isoften so unstable that solid contents are deposited to cause troublesand to impair the planeness. To avoid the problem, plural concentratedcellulose acylate solutions are simultaneously extruded from outletsonto the support. The thus-prepared thick film has excellent planeness.In addition, since the concentrated solutions are used, the film is soeasily dried that the productivity (particularly, production speed) canbe improved.

[0180] A plasticizer can be added into the cellulose acylate solution toenhance mechanical strength of the resultant film or to shorten the timefor drying. The plasticizer is, for example, a phosphate ester or acarboxylate ester. Examples of the phosphate ester used as theplasticizer include triphenyl phosphate (TPP) and tricresyl phosphate(TCP). Typical examples of the carboxylate ester are phthalate estersand citrate esters. Examples of the phthalate esters include dimethylphthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP),dioctyl phthalate (DOP), diphenyl phthalate (DPP) and diethylhexylphthalate (DEHP). Examples of the citrate esters include triethylo-acetylcitrate (OACTE) and tributyl o-acetylcitrate (OACTB). Besidesthe above, butyl oleate, methylacetyl ricinolate, dibutyl sebacate andvarious trimellitic esters are also usable. The plasticizers ofphosphate esters (DMP, DEP, DBP, DOP, DPP, DEHP) are preferred.Particularly preferred are DEP and DPP.

[0181] The content of the plasticizer is preferably in the range of 0.1to 25 wt. %, more preferably in the range of 1 to 20 wt. %, mostpreferably in the range of 3 to 15 wt. % based on the amount ofcellulose ester.

[0182] Further, a deterioration inhibitor (e.g., oxidation inhibitor,peroxide decomposer, radical inhibitor, metal inactivating agent, oxygenscavenger, amine) may be incorporated in the cellulose acetate film. Thedeterioration inhibitor is described in Japanese Patent ProvisionalPublication Nos. 3(1991)-199201, 5(1993)-1907073, 5(1993)-194789,5(1993)-271471 and 6(1994)-107854. The content of the deteriorationinhibitor is preferably in the range of 0.01 to 1 wt. %, more preferablyin the range of 0.01 to 0.2 wt. % based on the amount of the dope. Ifthe content is less than 0.01 wt. %, the deterioration inhibitor giveslittle effect. If it is more than 1 wt. %, the inhibitor often oozes out(bleeds out) to appear on the surface of the film. Particularlypreferred deterioration inhibitors are butylated hydroxytoluene (BHT)and tribenzylamine (TBA).

[0183] [Surface Treatment of Cellulose Acetate Film]

[0184] The cellulose acetate film is preferably subjected to surfacetreatment. Examples of the surface treatment include glow dischargetreatment, corona discharge treatment, ultraviolet (UV) treatment, flametreatment, and acid or alkali treatment. Further, an undercoating layeris preferably provided as described in Japanese Patent ProvisionalPublication No. 7(1995)-333433.

[0185] For ensuring the planeness of the film, the above treatments arecarried out preferably at a temperature not higher than Tg (not higherthan 150° C.).

[0186] In the case where the film is used as a transparent protectivefilm of the polarizing plate, the acid or alkali treatment is preferablycarried out to saponify the surface of the cellulose acetate film. Thattreatment enhances the adhesion between the polarizing plate and thefilm. The surface energy is preferably not less than 55 mN/m, morepreferably in the range of 60 to 75 mN/m.

[0187] The alkali saponification treatment is explained below.

[0188] That treatment comprises the steps of immersing. the film surfacein an alkaline solution, neutralizing with an acidic solution, washingwith water, and drying.

[0189] Examples of the alkaline solution include solutions of KOH andNaOH. The normality of hydroxyl ion is preferably in the range of 0.1 to3.0 N, more preferably in the range of 0.5 to 2.0 N. The temperature ofthe solution is preferably in the range of room temperature to 90° C.,more preferably in the range of 40 to 70° C.

[0190] From the viewpoint of productivity, the alkaline solution ispreferably applied on the film surface in place of immersing, and washedaway with water after saponification. As the solvent for the coatingalkaline solution, alcohols (e.g., IPA, n-butanol, methanol, ethanol)are preferred in consideration of wettability. Further, a dissolving aidsuch as water, propylene glycol. or ethylene glycol is preferably addedin the coating solution.

[0191] The surface energy can be measured by the contact angle method,the wet heating method or the adsorption method (these methods aredescribed in ‘The basic theory and application of wetting (written inJapanese)’, published by Realize Co., Ltd, 1989). The contact anglemethod is preferred. In that method, two solutions having known surfaceenergies are dropped onto the film. The contact angle of each drop ismeasured, and the surface energy of the film is calculated from themeasured contact angles. The contact angle is, by definition, an angle(including the drop) between the film surface and the tangent of thedrop surface at the crossing point.

[0192] <Optically Anisotropic Layer Comprising Liquid Crystal Compound>

[0193] [Liquid Crystal Compound]

[0194] The liquid crystal compound used in the optically anisotropiclayer may be either rod-like or discotic one. The compound may be apolymer liquid crystal or a monomer liquid crystal of low molecularweight. Further, a polymer in which liquid crystal molecules of lowmolecular weight are crosslinked and thereby which no longer behaves asliquid crystal is also usable. A discotic liquid crystal compound ismost preferably used in the invention.

[0195] Preferred examples of the rod-like liquid crystal compound aredescribed in Japanese Patent Publication No. 2000-304932. Examples ofthe discotic liquid crystal com-pound include benzene derivativesdescribed in C. Destrade et al., Mol. Cryst. vol. 71, pp. 111, (1981);truxene derivatives described in C. Destrade et al., Mol Cryst. vol.122, pp. 141. (1985), Physics lett. A, vol. 78, pp. 82, (1990);cyclohexane derivatives described in B. Kohn et al., Angew. Chem. vol.96, pp. 70, (1984); and macrocyclic compounds of azacrown-type orphenylacetylene-type described in J. M. Lehn et al., J. Chem. Commun.pp. 1794, (1985), and J. Zhang et al., J. Am. Chem. Soc. vol. 116,pp.2655, (1994). The above discotic compound generally has a structurein which the discotic structure unit is located at the center as aparent core and further straight chain groups such as alkyl, alkoxy andsubstituted benzoyl are radially substituted. The discotic compoundgenerally has the properties of liquid crystal, and hence includes acompound generally called discotic liquid crystal. As the discoticliquid crystal compounds, any compound can be used so long as it hasnegative uniaxial property and orientation property. Substance derivedfrom the discotic compound is not always the above-described compound.For example, the low molecular weight discotic liquid crystal compoundhaving a thermo- or photo-reactive group is polymerized by heat or lightto form a polymer that does not behave as liquid crystal. Such polymercan be also used in the invention. Preferred examples of the discoticliquid crystal compound are described in Japanese Patent ProvisionalPublication No. 8(1996)-50206.

[0196] The optically anisotropic layer is a birefringent layercontaining a compound having one or more discotic structure units, andthe discotic structure units preferably have planes inclined from aplane of the transparent support at an angle varying in the direction ofdepth of the optically anisotropic layer.

[0197] The above-described angle (inclined angle) of the plane ofdiscotic structure unit generally increases or decreases with increaseof distance in the direction of depth from the bottom of the opticallyanisotropic layer. The inclined angle preferably increases with increaseof the distance. Further, examples of variation of the inclined angleinclude continuous increase, continuous decrease, intermittent increase,intermittent decrease, variation containing continuous increase anddecrease,-and intermittent variation containing increase or decrease.The intermittent variation contains an area where the inclined angledoes not vary in the course of the thickness direction of the layer. Theinclined angle preferably totally increases or decreases in the layer,even if it does not vary in the course. The inclined angle morepreferably increases totally, and it is particularly preferred toincrease continuously.

[0198] The optically anisotropic layer can be generally prepared by thesteps of coating the orientation layer with a solution of the discoticcompound and other compounds dissolved in a solvent, drying, heating toa temperature for forming a discotic nematic phase, and cooling with theoriented condition (discotic nematic phase) kept. Otherwise, the layercan be prepared by the steps of coating the orientation layer with asolution of the discotic compound and other compounds (e.g.,polymerizable monomer, photo-polymerization initiator) dissolved in asolvent, drying, heating to a temperature for forming a discotic nematicphase, polymerizing the heated layer (e.g., by radiation of UV light)and cooling. The transition temperature from discotic nematic phase tosolid phase (temperature for heating) is preferably in the range of 70to 300° C., especially 70 to 170° C.

[0199] The inclined angle of the discotic unit on the support side canbe generally controlled by selecting the discotic compound or materialsof the orientation layer, or by selecting methods for the rubbingtreatment. On the other hand, for controlling the inclined angle of thediscotic unit on the surface side (air side), the discotic compound orother compounds (e.g., plasticizer, surface active agent, polymerizablemonomer and polymer) used together with the discotic compound areproperly selected. Further, the extent of variation of the inclinedangle can be also controlled by the above selections.

[0200] Any compound can be employed as the plasticizer, the surfaceactive agent and the polymerizable monomer, so long as it is compatiblewith the discotic compound and it gives variation of the inclined angleor dose not inhibit the discotic compound molecules from aligning.Preferred is a polymerizable monomer (e.g., a compound having a vinyl,vinyloxy, acryloyl or methacryloyl group). The compound is preferablyused in the amount of 1 to 50 wt. % (especially 5 to 30 wt. %) based onthe amount of the discotic compound. Preferred examples of thepolymerizable monomer include a acrylate having plural functionalgroups. The number of the functional groups is preferably three or more,more preferably four or more, most preferably six. Preferred examples ofthe acrylate having six functional groups include dipentaerythritolhexaacrylate. Two or more kinds of monomers having different numbers offunctional groups can be mixed to use in combination.

[0201] As the polymer, any polymer can be employed, so long as it iscompatible with the discotic compound and it gives variation of theinclined angle. Cellulose esters are preferably used. Examples of thecellulose esters include cellulose acetate, cellulose acetatepropionate,hydroxypropylcellulose, and cellulose acetatebutylate. The polymer isgenerally used in an amount of 0.1 to 10 wt. % (preferably 0.1 to 8.0wt. %, more preferably 0.1 to 5.0 wt. %) based on the amount of thediscotic compound, so as not to inhibit the discotic compound fromaligning.

[0202] The optical compensatory sheet in the invention comprises acellulose acetate film, an orientation layer and a discotic liquidcrystal layer, piled up in order. The orientation layer is preferablymade of crosslinked polymer, and preferably subjected to rubbingtreatment.

[0203] [Orientation Layer]

[0204] The orientation layer in the invention is made of crosslinked twopolymers. At least one of the polymers may be crosslinked by itself orwith a crosslinking agent. In other words, the polymers which originallyhave functional groups or to which functional groups are introduced arereacted with light, heat or pH variation to form the orientation layer;or otherwise linking groups are introduced by a reactive crosslinkingagent into the polymers so that the polymers are crosslinked to form theorientation layer.

[0205] In a normal process, a coating liquid containing the polymer and,if needed, the crosslinking agent is applied on the transparent support,and then heated to induce the crosslinking reaction. However, as long asthe resultant optical compensatory sheet has enough durability, thereaction may be caused at any stage from the step of coating the supportwith the coating liquid to the step of producing the resultant sheet. Inconsideration of orientation of the discotic compound (in the opticallyanisotropic layer) on the orientation layer, the crosslinking reactionis preferably caused sufficiently after the discotic compound isaligned. When the coating liquid containing the polymer and thecrosslinking agent is applied and heated to dry on the support, thecrosslinking reaction generally proceeds. (If the heating temperature islow, the reaction further proceeds when the discotic compound is heatedto the temperature to form discotic nematic phase.) After the appliedand dried layer is subjected to rubbing treatment to form an orientationlayer, another coating liquid containing the discotic compound isapplied and heated to the temperature to form discotic nematic phase.The heated liquid on the orientation layer is cooled to prepare theoptically anisotropic layer.

[0206] Polymers crosslinkable either by themselves or with crosslinkingagents can be used for forming the orientation layer in the invention.Some polymers are crosslinkable both by themselves and with crosslinkingagents, and of course they are also usable. Examples of the polymersinclude polymethyl metacrylate, acrylic acid/methacrylic acid copolymer,styrene/maleinimide copolymer, polyvinyl alcohol and denatured polyvinylalcohol, poly(N-methylolacrylamide), styrene/vinyltoluene copolymer,chlorosulfonated polyethylene, nitrocellulose, polyvinyl chloride,chlorinated poly-olefin, polyester, polyimide, vinyl acetate/vinylchloride copolymer, ethylene/vinyl acetate copolymer,carboxymethylcellulose, polyethylene, polypropylene, polycarbonate, andorganic substances such as silan coupling agents. Preferred examples arewater-soluble polymers such as poly(N-methylolacrylamide),carboxymethylcellulose, gelatin, polyvinyl alcohol and denaturedpolyvinyl alcohol. Gelatin, polyvinyl alcohol and denatured polyvinylalcohol are more preferred, and polyvinyl alcohol and denaturedpolyvinyl alcohol are particularly preferred.

[0207] It is most preferred to use two kinds of polyvinyl alcohols ordenatured polyvinyl alcohols having different polymerization degrees.

[0208] The saponification degree of the polyvinyl alcohol is in therange of 70 to 100%, preferably in the range of 80 to 100%, morepreferably in the range of 85 to 95%. The polymerization degree ispreferably in the range of 100 to 3,000. Examples of the denaturedpolyvinyl alcohol include polyvinyl alcohols denatured bycopolymerization (introduced denaturing group: COONa, Si(OX)₃,N(CH₃)₃.Cl, C₉H₁₉COO, SO₃Na, C₁₂H₂₅, etc.), by chain transfer(introduced denaturing group: COONa, SH, C₁₂H₂₅, etc.) and by blockpolymerization (introduced denaturing group: COOH, CONH₂, COOR, C₆H₅,etc.). Non- or denatured polyvinyl alcohols having saponificationdegrees of 80 to 100% is preferred, and alkylthio-denatured polyvinylalcohols having saponification degrees of 85 to 95% are particularlypreferred. With respect to the denatured polyvinyl alcohols, JapanesePatent Provisional Publication No. 8(1996)-338913 describes in detailtheir syntheses, measurement of visible absorption spectra and a methodfor determining the introducing ratios.

[0209] Examples of the crosslinking agent include aldehydes (e.g.,formaldehyde, glyoxal, glutaraldehyde), N-methylol compounds (e.g.,dimethylol urea, methyloldimethylhydantoin), dioxane derivatives (e.g.,2,3-dihydroxydioxane), compounds that works when the carboxylic group isactivated (e.g., carbenium, 2-naphthalenesulfonate,1,1-bispyrrolidino-1-chloropyridinium,1-morpholinocarbonyl-3-(sulfonatoaminomethyl), active vinyl compounds(e.g., 1,3,5-triacryloyl-hexahydro-s-triazine,bis-(vinylsulfone)methane,N,N′-methylenebis-[β-(vinylsulfonyl)propionamide], active halogencompounds (e.g., 2,4-dichloro-6-hydroxy-s-triazine), isooxazoles anddialdehyde starch. These are preferably used together with water-solublepolymers, particularly polyvinyl alcohol and denatured polyvinylalcohols (including the above-described denatured polyvinyl alcohols).Two or more crosslinking agents may be used in combination. Inconsideration of productivity, reactive aldehydes are preferred.Particularly preferred is glutaraldehyde.

[0210] The more the crosslinking agent is added, the stronger moistureresistance the resultant layer has. However, if the agent isincorporated in an amount of 50 wt. % or more based on the amount of thepolymer, the resultant orientation layer shows poor orienting effect.Accordingly, the amount of the crosslinking agent is in the range ofpreferably 0.1 to 20 wt. %, more preferably 0.5 to 15 wt. % based on theamount of the polymer. The amount of non-reacted crosslinking agentremaining in the orientation layer is preferably not more than 1.0 wt.%, more preferably not more than 0.5 wt. % based on the amount of theorientation layer. If the layer contains the non-reacted agent in anamount of more than 1.0 wt. %, the layer has poor durability. A liquidcrystal display comprising such orientation layer often suffers troublesof reticulation if used for a long time or left under hot and humidcondition.

[0211] The orientation layer can be formed by the steps of applying acoating liquid containing the above polymer and the crosslinking agentonto the transparent support, heating to dry (and to crosslink), andsubjecting to rubbing treatment. As described above, the crosslinkingreaction may be caused at any step after applying the coating liquid. Inthe case where a water-soluble polymer such as polyvinyl alcohol isused, the coating solution is preferably prepared from a mixed solventof water and an organic solvent having defoaming character (e.g.,methanol). The ratio of water/methanol is normally in the range of 0:100to 99:1, preferably in the range of 0:100 to 91:9. Because of defoamingcharacter of the organic solvent, defects on the orientation layer areremarkably decreased, and accordingly the optically anisotropic layerhas an improved surface. As the coating method, known methods such asspin-coating, dip-coating, curtain-coating, extrusion-coating,bar-coating and E-type coating can be adopted. The E-type coating methodis particularly preferred. The thickness of the layer is preferably inthe range of 0.1 to 10 μm. The applied layer is dried at a temperatureof 20 to 110° C. For ensuring sufficient crosslinking, the temperatureis preferably in the range of 60 to 100° C., more preferably in therange of 80 to 100° C. The time for drying is in the range of 1 minuteto 36 hours, preferably in the range of 5 minutes to 30 minutes. The pHis also preferably adjusted at an optimal value according to the usedcrosslinking agent. If glutaraldehyde is used as the crosslinking agent,the pH is preferably in the range of 4.5 to 5.5, more preferably at 5.0.

[0212] The orientation layer is provided on the transparent support oran undercoating layer. After the above-described polymer layer iscrosslinked, the surface of the layer is subjected to rubbing treatment.The orientation layer determines the aligning direction of discoticliquid crystal compound provided thereon.

[0213] The rubbing treatment can be conducted in the manner adoptedwidely in aligning liquid crystal molecules of LCD. The surface of thelayer is rubbed with paper, cloth (gauze, felt, nylon, polyester) orrubber along a certain direction, to give the aligning function.Generally, the layer is rubbed several times with cloth on which fibershaving the same length and thickness are provided.

[0214] <Transparent Support on which Optically Anisotropic LayerComprising Liquid Crystal Compound is Provided>

[0215] The material of the support is not restricted as long as it ismade of highly transparent plastic resin. A preferred material iscellulose acetate, which is also used for a protective film of thepolarizing plate. The transparent support may be optically uniaxial orbiaxial.

[0216] The transparent support, on which the optically anisotropic layeris provided, optically plays an important role. Therefore, theretardation value Re of the support is preferably in the range of 0 to200 nm. The Rth of the support is preferably in the range of 70 to 400nm.

[0217] If the liquid crystal display comprises two optically anisotropiccellulose acetate films, the Rth value of each film is preferably in therange of 70 to 250 nm.

[0218] If the liquid crystal display comprises one optically anisotropiccellulose acetate film, the Rth value of the film is preferably in therange of 150 to 400 nm.

[0219] The cellulose acetate film preferably has a birefringent index[Δn: nx−ny] of 0.00 to 0.002. The birefringent index along the filmthickness [(nx+ny)/2−nz] is preferably in the range of 0.001 to 0.04.

[0220] The retardation value Re is determined according to the formula:Re=(nx−ny)×d in which nx is a refractive index along the show axis inthe film plane (the maximum refractive index in the film plane), and nyis a refractive index perpendicular to the show axis in the film plane.

[0221] The retardation value Rth is determined according to the formula:Rth={(nx+ny)/2−nx}×d in which nx is a refractive index along the showaxis in the film plane (the maximum refractive index in the film plane),ny is a refractive index along the traveling axis in the film plane (theminimum refractive index in the film plane), nz is a refractive indexalong the depth of the film, and d is thickness of the film in terms ofnm.

[0222] [Polarizing Plate]

[0223] The polarizing plate comprises two transparent protective filmsand a polarizing membrane provided between the films. The diffusing filmor anti-reflection film of the invention can be used as one of theprotective films. A normal cellulose acetate film can be used as theother protective film.

[0224] Examples of the polarizing membrane include an iodine polarizingmembrane, a polyene polarizing membrane and a dichromatic dye polarizingmembrane. The iodine polarizing membrane and the dye polarizing membraneare generally prepared from polyvinyl alcohol films.

[0225] The transparent substrate of the diffusing film and the celluloseacetate film are placed so that the slow axes of the films may beessentially parallel to the transmission axis of the polarizingmembrane.

[0226] It has been found that the moisture-permeability of theprotective film is important for production of the polarizing plate. Inproducing the polarizing plate, the polarizing membrane and theprotective film are laminated with an aqueous adhesive, and then thesolvent of the adhesive is diffused into the film to dry. The higherpermeability the film has, the more-rapidly it is dried. Accordingly,the productivity of the polarizing plate is improved. However, if thepermeability is too high, the outer moisture is liable to come into themembrane to impair polarizability if the liquid crystal display is usedunder humid condition.

[0227] The moisture-permeability depends upon various conditions such asthickness, free volume, and hydrophilicity (hydrophobicity) of thepolymer film (and polymerizable liquid crystal compound).

[0228] The protective film in the polarizing plate has amoisture-permeability preferably in the range of 100 to 1,000 g/m²·24hours, more preferably in the range of 300 to 700 g/m²·24 hours.

[0229] In the film forming process, conditions and procedures such asrip flow, line speed, stretching and/or compressing are adequatelyselected to control the thickness of the transparent substrate. Sincethe moisture-permeability depends on the materials, the thickness may becontrolled so that the preferable permeability can be obtained.

[0230] Also in the film forming process, drying conditions such as timeand temperature are suitably determined to control the free volume ofthe transparent substrate. Since the moisture-permeability depends onthe materials, the free volume may be controlled so that the preferablepermeability can be obtained.

[0231] The hydrophilicity (hydrophobicity) of the transparent substratecan be controlled with additives. If hydrophilic additives are containedin the above free volume, the permeability is increased. If hydrophobicadditives are added, the permeability is decreased.

[0232] The moisture-permeability can be thus independently controlled,and thereby the polarizing plate having optical compensatory functioncan be produced at small cost with high productivity.

[0233] The polarizing plate preferably comprises the diffusing film orthe anti-reflection film of the invention, a polarizer, and an opticallyanisotropic layer, piled up in order.

[0234] The optically anisotropic layer may be provided on a polymerfilm, and may contain a discotic liquid crystal compound or a rod-likeliquid crystal compound. A discotic liquid crystal compound ispreferred. In preparing the optically anisotropic layer, molecules ofthe discotic (or rod-like) liquid crystal compound are aligned and thethus-formed alignment is fixed.

[0235] Since the discotic liquid crystal molecules generally give largebirefringence and have various alignment forms, an optically anisotropiclayer prepared from the discotic liquid crystal molecules has a specificoptical characteristic that cannot be obtained from the conventionalstretched birefringent polymer film. The optically anisotropic layercomprising the discotic liquid crystal compound is described in JapanesePatent Provisional Publication No. 6(1996)-214116, U.S. Pat. Nos.5,583,679 and 5,646,703, and West German Patent Publication No.3911620A1.

[0236] [Liquid Crystal Display]

[0237] The diffusing film, the anti-reflection film or the polarizingplate of the invention is preferably used in a liquid crystal display.They are preferably placed on the top surface of the display.

[0238] A liquid crystal display of TN, MVA, OCB, ECB or CPA modecomprises two polarizing plates and a liquid crystal cell providedbetween them. The liquid crystal cell comprises a pair of electrodesubstrates and liquid crystal molecules placed between them.

[0239] One optically anisotropic layer is placed between the cell andone of the polarizing plates. Otherwise, two optically anisotropiclayers are placed on both sides of the cell (i.e., each layer is placedbetween the cell and each polarizing plate).

[0240] The liquid crystal cell works preferably according to VA mode,OCB mode, TN mode, ECB mode or CPA mode.

[0241] In a liquid crystal cell of VA mode, rod-like liquid crystalmolecules are essentially vertically aligned while voltage is notapplied.

[0242] The liquid crystal cell of VA mode include some types:

[0243] (1) a liquid crystal cell of VA mode in a narrow sense (describedin Japanese Patent Provisional Publication No. 2(1990)-176625), in whichrod-like liquid crystal molecules are essentially vertically alignedwhile voltage is not applied, and the molecules are essentiallyhorizontally aligned while voltage is applied;

[0244] (2) a liquid crystal cell of MVA mode (described in SID97, Digestof tech. Papers, 28(1997), 845), in which the VA mode is modified to bemulti-domain type so as to enlarge the viewing angle;

[0245] (3) a liquid crystal cell of n-ASM mode (described in NipponEkisho Toronkai [Liquid crystal forum of Japan], Digest of tech. Papers(1998), 58-59), in which rod-like liquid crystal molecules areessentially vertically aligned while voltage is not applied, and themolecules are essentially oriented in twisted multi-domain alignmentwhile voltage is applied;

[0246] (4) a liquid crystal cell of SURVAIVAL mode (published in LCDinternational 98); and

[0247] (5) a liquid crystal cell of CPA mode (published in SID01), inwhich the molecules are oriented in twisted alignment when voltage isapplied.

[0248] The liquid crystal cell of OCB mode is a liquid crystal cell ofbend alignment mode in which rod-like liquid crystal molecules in upperpart-and ones in lower part are essentially reversely (symmetrically)aligned. A liquid crystal display having the liquid crystal cell of bendalignment mode is disclosed in U.S. Pat. Nos. 4,583,825 and 5,410,422.Since rod-like liquid crystal molecules in upper part and ones in lowerpart are symmetrically aligned, the liquid crystal cell of bendalignment mode has self-optical compensatory function. Therefore, thismode is referred to as OCB (optically compensatory bend) mode. Theliquid crystal display of bend alignment mode has an advantage ofresponding rapidly.

[0249] In a liquid crystal cell of TN mode, rod-like liquid crystalmolecules are essentially horizontally aligned while voltage is notapplied, and oriented in twisted alignment with a twisted angle of 60 to1200.

[0250] In a liquid crystal cell of ECB mode, rod-like liquid crystalmolecules are essentially horizontally aligned while voltage is notapplied.

[0251] The liquid crystal cells of TN mode and ECB mode are widely usedin color TFT liquid crystal displays, and hence are described in manypublications.

EXAMPLE 1

[0252] In a mixed solvent of methyl ethyl ketone/methyl isobutyl ketone(20/80, by weight), 100 weight parts of zirconium oxide-dispersed hardcoat liquid (Desolite KZ-7114A, JSR Co., Ltd.), 43 weight parts oftransparent resin (DPHA, Nippon Kayaku Co., Ltd.) and 5 weight parts ofhardening initiator (Irgacure 184, Ciba-Geigy) were mixed and dissolved(dispersed) with stirring by means of air-disperser. The prepared liquidwas applied, dried, and then exposed to ultraviolet light to harden thelayer. The thus-formed layer had the refractive index of 1.64.

[0253] To the above prepared liquid, 8.5 weight parts of crosslinkedpolystyrene beads (SX350, Soken Kagaku Co., Ltd.; particles size: 3.5μm; refractive index: 1.61) as the matting particles and 15 weight partsof gelatin as the scatterers were mixed and dispersed. The solid contentof the mixture was controlled with methyl ethyl ketone/methyl isobutylketone (20/80, by weight) at 45%. The thus-prepared mixture wasemulsified by means of a dissolver at 10,000 rpm for about 15 minutes.The prepared emulsion was applied on a triacetyl cellulose film (TD-80U,Fuji Photo Film Co., Ltd.) to form a layer having the dry thickness of4.0 μm. The layer was dried, and then exposed to ultraviolet light(illuminance: 400 mW/cm², exposure: 300 mJ/cm²) emitted from anair-cooled metal halide lamp of 160 W/cm (Eyegraphics Co., Ltd.) toharden the layer. Thus, a diffusing film (HKF-01) was prepared.

[0254] The haze value of the film HKF-01 was determined by means of ameasuring apparatus (HR-100, Murakami Shikisai Gijutsu-kenkyujo Co.,Ltd,) according to JIS-K-7105. As a result, it was found that the hazemeasured along the normal was 10% and that the haze measured in thedirection inclined at 30° from the normal was 40%. Those values weresuitable for the invention.

[0255] The film HKF-01 had the surface roughness of 0.15 μm, and theclearness of transmitted image was 55%.

[0256] The scatterers (transparent fine particles) had the average sizesof 15 μm and 3 μm in the sections parallel and perpendicular to thenormal, respectively. Those having particle sizes of 0.1 to 50 μm hadthe average aspect ratio of 5 and the refractive index of 1.44.

[0257] For determining the aspect ratio of the scatterers, first thesizes in the section perpendicular to the normal were measured by meansof a transmission optical microscope. The film was then cut with amicrotome (CM1510, Leica), and the section was observed through anelectron microscope (S3500N, Hitachi Science Systems Co., Ltd.) tomeasure the sizes in the section parallel to the normal.

EXAMPLE 2

[0258] As the transparent resin constituting the scattering layer, 150weight parts of 65 wt. % zirconium oxide-dispersed gelatin was added inwater. The obtained liquid was applied to form a layer having therefractive index of 1.64.

[0259] To the above liquid, 8.5 weight parts of crosslinked polystyrenebeads (SX350, Soken Kagaku Co., Ltd.; particles size: 3.5 μm; refractiveindex: 1.61) as the matting particles and 20 weight parts of transparentmonomer (a mixture of 43 weight parts of transparent resin [DPHA, NipponKayaku Co., Ltd.] and 5 weight parts of hardening initiator [Irgacure184, Ciba-Geigy]) were mixed. The solid content of the prepared liquidwas controlled with water at 50%. The thus-prepared liquid wasemulsified by means of a dissolver at 10,000 rpm for about 15 minutes.The prepared emulsion was applied on a triacetyl cellulose film (TD-80U,Fuji Photo Film Co., Ltd.) to form a layer having the dry thickness of3.5 μm. The layer was dried, and then exposed to ultraviolet light(illuminance: 400 mW/cm², exposure: 300 mJ/cm²) emitted from anair-cooled metal halide lamp of 160 W/cm (Eyegraphics Co., Ltd.) toharden the layer. Thus, a diffusing film (HKF-02) was prepared. In theprepared film, the transparent monomer was polymerized with thehardening initiator to form fine particles that served as thescatterers.

[0260] The haze value of the film HKF-02 was determined by means of ameasuring apparatus (HR-100, Murakami Shikisai Gijutsu-kenkyujo Co.,Ltd,) according to JIS-K-7105. As a result, it was found that the hazemeasured along the normal was 7% and that the haze measured in thedirection inclined at 30° from the normal was 54%. Those values weresuitable for the invention.

[0261] The film HKF-02 had the surface roughness of 0.11 μm, and theclearness of transmitted image was 65%.

[0262] The scatterers (transparent fine particles) had the average sizesof 10 μm and 0.5 μm in the sections parallel and perpendicular to thenormal, respectively. Those having particle sizes of 0.1 to 50 μm hadthe average aspect ratio of 20 and the refractive index of 1.51.

[0263] (Preparation of Coating Solution for Low Refractive Index Layer)

[0264] Into 93 g of a thermo-crosslinkable fluorine-containing polymer(JN-7228, JSR Co., Ltd.; refractive index: 1.42), 8 g of SiO₂ soldispersed in methyl ethyl ketone (MEK-ST, Nissan Chemicals Co., Ltd.;solid content: 30 wt. %, average particle size of SiO₂: 10 to 20 nm) and100 g of methyl ethyl ketone were added and stirred. The obtained liquidwas filtrated through a propylene filter (porous size: 1 μm) to preparea coating solution for low refractive index layer.

EXAMPLE 3

[0265] The above-prepared coating solution was applied on the scatteringlayer of the diffusing film (HKF-01) by means of a wire-bar coater,dried at 80° C., and further heated at 120° C. for 10 minutes tocrosslink. Thus, a low refractive index layer (thickness: 0.096 μm) wasformed to produce an anti-reflection film (HKHB-01).

EXAMPLE 4

[0266] The coating solution for low refractive index layer was appliedon the scattering layer of the diffusing film (HKF-02) by means of awire-bar coater, dried at 80° C., and further heated at 120° C. for 10minutes to crosslink. Thus, a low refractive index layer (thickness:0.096 μm) was formed to produce an anti-reflection film (HKHB-02).

COMPARISON EXAMPLE 1

[0267] As the transparent resin constituting the scattering layer, 100weight parts of UV curable resin (Desolite Z-7526, JSR Co., Ltd.;refractive index: 1.51) was used. To the resin, 12 weight parts ofbenzoguanamine-melamine-formaldehyde beads (Nippon Catalyst Co., Ltd.;particles size: 0.5 μm; refractive index: 1.68) as the transparent fineparticles and 11 weight parts of crosslinked polystyrene beads (SX350H,Soken Kagaku Co., Ltd.; particles size: 3.5 μm; refractive index: 1.61)were mixed. The solid content of the prepared liquid was controlled withmethyl ethyl ketone/acetone (40/60) at 50%. The thus-prepared liquid wasapplied on a triacetyl cellulose film (TD-80U, Fuji Photo Film Co.,Ltd.) to form a layer having the dry thickness of 3.0 μm. The layer wasdried, and then exposed to ultraviolet light (illuminance: 400 mW/cm²,exposure: 300 mJ/cm²) emitted from an air-cooled metal halide lamp of160 W/cm (Eyegraphics Co., Ltd.) to harden the layer. Thus, a diffusingfilm was prepared.

[0268] The haze value of the prepared film was determined by means of ameasuring apparatus (HR-100, Murakami Shikisai Gijutsu-kenkyujo Co.,Ltd,) according to JIS-K-7105. As a result, it was found that the hazewas 50%. The measured value was suitable for the invention. However, thefilm had the surface roughness Ra of 0.35 μm, and the clearness oftransmitted image was 12%.

[0269] (Evaluation of Diffusing Film)

[0270] The prepared diffusing films were evaluated in the followingmanner.

[0271] (1) Mirror Reflectance

[0272] The mirror reflectance of light in the wavelength region of 380to 780 nm coming at the incident angle of 5° was measured at thereflection angle of −5° by means of a spectrophotometer (V-550, JapanSpectrum Co., Ltd.) equipped with an adaptor ARV-474. The averagereflectance in the wavelength range of 450 to 650 nm was calculated, andthereby the ability of anti-reflection was evaluated.

[0273] (2) Haze

[0274] The haze of each prepared film was measured with a haze meter(MODEL 1001DP, Nippon Denshoku kogyo Co., Ltd.).

[0275] (3) Hardness Evaluated with Pencil

[0276] The scratch resistance of each sample film was estimated in termsof hardness evaluated with a pencil according to JIS-K-5400. Theanti-reflection film was left under the conditions of 25° C. and 60%RHfor 2 hours, and then scratched with a testing pencil of 3H according toJIS-S-606 (loading weight: 1 kg). On the basis of the result, the samplewas classified into the following three grades:

[0277] A: no scratch was observed,

[0278] B: one or two scratches were observed, and

[0279] C: three or more scratches were observed

[0280] under the condition of n=5.

[0281] (4) Contact Angle

[0282] The resistance against stain (how hard the film catches fingerprints) was estimated in terms of contact angle with water. Each samplewas left under the conditions of 25° C. and 60%RH for 2 hours, and thenthe contact angle was measured.

[0283] (5) Coefficient of Kinetic Friction

[0284] The surface slipperiness was estimated in terms of coefficient ofkinetic friction. Each sample was left under the conditions of 25° C.and 60%RH for 2 hours, and then its coefficient of kinetic friction wasmeasured by means of a kinetic friction tester (HEIDON-14) with a 5 mmφstainless steel ball (weight: 100 g, speed: 60 cm/minute).

[0285] (6) Anti-Glaringness

[0286] A fluorescent lamp (8,000 cd/m²) was reflected in each preparedanti-glare film, and it was observed how blurred the reflected imagewas. On the basis of the observation, the sample was classified into thefollowing four grades:

[0287] A: the outline of the image was completely blurred,

[0288] B: the outline of the image was slightly blurred,

[0289] C: the image was blurred, but the outline could be recognized,and

[0290] D: the image was blurred little.

[0291] (7) Surface Resistance

[0292] The surface resistance of each sample was measured according tothe disc electrode method, and thereby it was confirmed that all sampleshad surface resistance of 1×10¹² Ω/cm or more.

[0293] (8) Electrification when Vertically Peeled

[0294] The electrification of each prepared film when vertically peeledfrom a triacetyl cellulose film was measured in the manner describedabove.

[0295] (9) Dustproof (How Hard to Catch Dust)

[0296] Each sample film was laminated on a glass plate, and discharged.After the film was rubbed with cloth (Tracy, Toray Industries, Inc.) 10times, fine powder of Styrofoam (false dust) was sprinkled on the wholefilm. The film was then made to stand, and it was observed how much thefalse dust fell off. On the basis of the observation, the sample wasclassified into the following four grades:

[0297] A: almost all the false dust fell off,

[0298] B: 80% or more of the false dust fell off,

[0299] C: 50% or more of the false dust fell off, and

[0300] D: 50% or more of the false dust remained on the film.

[0301] The results are set forth in Table 1. TABLE 1 SurfaceElectrification Dust Mirror Grade of Coefficient Diffusing Haze (%)roughness when vertically proof reflec- anti-glare of kinetic Contactfilm Normal 60° (μm) peeled (pc) grade tance function friction angleExample 3 10 40 0.15 +50 A 1.8% A 0.08 103° Example 4  7 54 0.11 −50 A1.1% A 0.08 103° Comp. Ex. 1 50 55 0.35 −500 D 4.0% A — —

[0302] The results in Table 1 indicate that the diffusion films ofExamples 3 and 4 were excellent in anti-glaringness and anti-reflection.Further, they had good film characters such as hardness evaluated withpencil (both had the grade A), contact angle (both showed large contactangles), and slipperiness (both had small coefficients of kineticfriction). They also gave weakly colored images. On the other hand,since the film of Comparison Example 1 had no low refractive indexlayer, it could not fully prevent reflection.

[0303] Polarizing plates equipped with the above films of Examples wereprepared. Each polarizing plate was installed in a liquid crystaldisplay, and evaluated.

[0304] <Preparation of Polarizing Plate on Observer Side SHB-01>

[0305] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The film HKHB-01 was saponified, andlaminated on one surface of the polarizing membrane with polyvinyladhesive so that the transparent substrate (triacetyl cellulose film) ofthe HKHB-01 might be contact with the membrane. A commercially availableoptical compensatory sheet [WVSA12B, Fuji Photo Film Co., Ltd.](whichhas an optically anisotropic layer comprising liquid crystal compound)was also saponified, and laminated on the other surface of the membranewith polyvinyl adhesive so that the support of the sheet might becontact with the membrane. Thus, a polarizing plate on observer side(SHB-01) was prepared.

[0306] <Preparation of Polarizing Plate on Observer Side SHB-02>

[0307] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. The film HKHB-02 was saponified, andlaminated on one surface of the polarizing membrane with polyvinyladhesive so that the transparent substrate (triacetyl cellulose film) ofthe HKHB-02 might be contact with the membrane. A commercially availableoptical compensatory sheet [WVSA12B, Fuji Photo Film Co., Ltd.](whichhas an optically anisotropic layer comprising liquid crystal compound)was also saponified, and laminated on the other surface of the membranewith polyvinyl adhesive so that the support of the sheet might becontact with the membrane. Thus, a polarizing plate on observer side(SHB-02) was prepared.

[0308] <Preparation of Polarizing Plate on Backlight Side BHB-01>

[0309] Iodine was adsorbed on a stretched polyvinyl alcohol film toprepare a polarizing membrane. A commercially available triacetylcellulose film (Fujitac TD80, Fuji Photo Film Co., Ltd.) was saponified,and laminated on one surface of the polarizing membrane with polyvinyladhesive. A commercially available optical compensatory sheet [WVSA12B,Fuji Photo Film Co., Ltd.](which has an optically anisotropic layercomprising liquid crystal compound) was also saponified, and laminatedon the other surface of the membrane with polyvinyl adhesive so that thecellulose acetate film might be contact with the membrane. Thus, apolarizing plate on backlight side (BHB-01) was prepared.

EXAMPLE 5

[0310] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of TN mode (6E-A3, Sharp Corporation).In place of the removed polarizing plates, the polarizing plate (SHB-01)was laminated on the observer side surface with adhesive so that theoptical compensatory sheet might be on the liquid crystal cell side. Onthe backlight side, the above-prepared polarizing plate on backlightside (BHB-01) was laminated with adhesive so that the opticalcompensatory sheet might be on the liquid crystal cell side. Thepolarizing plate on the observer side and that on the backlight sidewere placed so that the transmission axes of the observer side plate andthe backlight side plate might be arranged in 0 mode. Thus, the liquidcrystal display was prepared.

[0311] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of the eight tones of black (L1) to white (L8) was displayed.Further, the coloring of the image in a neutral tone (L3) was measured.The results are set forth in Table 2.

EXAMPLE 6

[0312] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of TN mode (6E-A3, Sharp Corporation).In place of the removed polarizing plates, the polarizing plate (SHB-02)was laminated on the observer side surface with adhesive so that theoptical compensatory sheet might be on the liquid crystal cell side. Onthe backlight side, the above-prepared polarizing plate on backlightside (BHB-01) was laminated with adhesive so that the opticalcompensatory sheet might be on the liquid crystal cell side. Thepolarizing plate on the observer side and that on the backlight sidewere placed so that the transmission axes of the observer side plate andthe backlight side plate might be arranged in 0 mode. Thus, the liquidcrystal. display was prepared.

[0313] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of the eight tones of black (L1) to white (L8) was displayed.Further, the coloring of the image in a neutral tone (L3) was measured.The results are set forth in Table 2.

COMPARISON EXAMPLE 1

[0314] A pair of polarizing plates were removed from a commerciallyavailable liquid crystal display of TN mode (6E-A3, Sharp Corporation).In place of the removed polarizing plates, commercially availablepolarizing plates (LL-82-12WNA, Sunritz Co., Ltd.) were laminated. Thepolarizing plate on the observer side and that on the backlight sidewere placed so that the transmission axes of the observer side plate andthe backlight side plate might be arranged in 0 mode. Thus, the liquidcrystal display was prepared.

[0315] The viewing angle of the prepared liquid crystal display wasmeasured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM)when each of the eight grade levels of black (L1) to white (L8) wasdisplayed. Further, the coloring of the image in a neutral grade level(L3) was measured. The results are set forth in Table 2. TABLE 2 LiquidViewing angle giving a contrast ratio of 10 crystal or more withoutreversing black grade levels display Upward Downward Left-rightwardExample 5 80° 75° 160° Example 6 75° 65° 160° Comp. Ex. 2 30° 15° 100°

[0316] The liquid crystal displays of Examples 5 and 6 gave imageshaving the same qualities (brightness, contrast) as the image given bythe display of Comparison Example 2, and this means that the displays ofExamples 5 and 6 enlarged the viewing angles without impairing the imagequalities. Thus, the anti-reflection film, the polarizing plate and theliquid crystal display according to the invention have excellent viewingangle characters.

EXAMPLE 7

[0317] In a mixed solvent of methyl ethyl ketone/methyl isobutyl ketone(20/80, by weight), 100 weight parts of silica-dispersed hard coatliquid (Desolite Z-7526, JSR Co., Ltd.), 43 weight parts of transparentresin (DPHA, Nippon Kayaku Co., Ltd.) and 5 weight parts of hardeninginitiator (Irgacure 184, Ciba-Geigy) were mixed and dispersed withstirring by means of air-disperser. The prepared liquid was applied,dried, and then exposed to ultraviolet light to harden the layer. Thethus-formed layer had the refractive index of 1.51.

[0318] To the above liquid, 8.5 weight parts of crosslinked polystyrenebeads (SX350, Soken Kagaku Co., Ltd.; particles size: 3.5 μm; refractiveindex: 1.61) as the matting particles and 15 weight parts of finecolumnar stacks of barium ferrite (BF2700, Titanium Industries Co.,Ltd.) as the scatterers were mixed. The solid content of the preparedliquid was controlled at 45%. The thus-prepared liquid was applied on atriacetyl cellulose film (TD-80U, Fuji Photo Film Co., Ltd.) to form alayer having the dry thickness of 4.0 μm. The layer was dried, and thenexposed to ultraviolet light (illuminance: 400 mW/cm², exposure: 300mJ/cm²) emitted from an air-cooled metal halide lamp of 160 W/cm(Eyegraphics Co., Ltd.) to harden the layer. Thus, a diffusing film(HKF-03) was prepared. In the prepared film, the transparent monomer waspolymerized with the hardening initiator to form fine particles thatserved as the scatterers.

[0319] The haze value of the film HKF-03 was determined by means of ameasuring apparatus (HR-100, Murakami Shikisai Gijutsu-kenkyujo Co.,Ltd,) according to JIS-K-7105. As a result, it was found that the hazemeasured along the normal was 9% and that the haze measured in thedirection inclined at 30° from the normal was 60%. Those values weresuitable for the invention.

[0320] The film HKF-03 had the surface roughness of 0.13 μm, and theclearness of transmitted image was 59%.

[0321] The scatterers (transparent fine particles) had the average sizesof 0.05 μm and 5 μm in the sections parallel and perpendicular to thenormal, respectively. Those had the average aspect ratio of 0.01.

[0322] For determining the aspect ratio of the scatterers, first thesizes in the section perpendicular to the normal were measured by meansof a transmission optical microscope. The film was then cut with amicrotome (CM1510, Leica), and the section was observed through anelectron microscope (S3500N, Hitachi Science Systems Co., Ltd.) tomeasure the sizes in the section parallel to the normal.

I claim:
 1. A diffusing film comprising a transparent resin in whichscatterers are dispersed, wherein the difference between the refractiveindex of the transparent resin and that of the scatterers is in therange of 0.04 to 1.5, and wherein scatterers are flat particles havingparticle sizes in the range of 0.1 to 50 μm.
 2. The diffusing film ofclaim 1, wherein the scatterers are tabular particles.
 3. The diffusingfilm of claim 2, wherein the ratio of the average size of scatterers ina section parallel to the film plane to that in a section perpendicularto the film plane is 2 or more.
 4. The diffusing film of claim 1,wherein the scatterers are columnar or rod-like particles.
 5. Thediffusing film of claim 4, wherein the ratio of the average size ofscatterers in the section parallel to the film plane to that in thesection perpendicular to the film plane is 0.5 or less.
 6. The diffusingfilm of claim 1, wherein at least one surface of the diffusing film hasa surface roughness of 0.05 to 0.18 μm.
 7. The diffusing film of claim1, wherein the transparent resin further contains a matting agent in theform of fine particles, and the difference between the refractive indexof the transparent resin and that of the matting agent is less than0.04.
 8. The diffusing film of claim 1, wherein the transparent resinfurthermore contains superfine particles whose particle sizes are lessthan 0.1 μm.
 9. The diffusing film of claim 1, wherein a scatteringlayer comprising the transparent resin and the scatterers dispersedtherein is provided on a transparent substrate.
 10. The diffusing filmof claim 9, wherein the scattering layer has a thickness of 2.0 to 6.0μm.
 11. The diffusing film of claim 9, wherein a low-refractive indexlayer is further provided on the scattering layer.
 12. The diffusingfilm of claim 11, wherein an incident ray coming into the low-refractiveindex layer at the incident angle of 50° is reflected in an averagemirror reflectance of 2.5% or less in the wavelength region of 450 to650 nm.
 13. A process for preparation of a diffusing film comprising thesteps of: dissolving or dispersing a transparent resin and scattererswhose refractive index differs from that of the transparent resin by0.04 to 1.5, in a mixture of a solvent having a function of dissolving atransparent substrate and another solvent having a function of notdissolving the substrate, to prepare a coating solution; applying thesolution onto the transparent substrate; and drying the solution to forma scattering layer containing flat scatters which have particle size of0.1 to 50 μm.
 14. The process of claim 13, wherein the scattering layerhas a thickness of 2.0 to 6.0 μm, and the transparent resin soaks into adepth of 0.01 to 1.0 μm, in the substrate.
 15. The process of claim 13,wherein the substrate is made of cellulose acetate, and the solventdissolving the substrate contains a ketone.
 16. A polarizing platecomprising a pair of protective films and a polarizing membrane providedbetween them, wherein one of the protective films is a diffusing filmcomprising a transparent resin in which scatterers are dispersed,wherein the difference between the refractive index of the transparentresin and that of the scatterers is in the range of 0.04 to 1.5, andwherein scatterers are flat particles having particle sizes in the rangeof 0.1 to 50 μm.
 17. The polarizing plate of claim 16, wherein anoptically anisotropic layer comprising a liquid crystal compound isprovided on the other protective film.
 18. The polarizing plate of claim17, wherein the liquid crystal compound is a discotic compound.
 19. Aliquid crystal display of transmission type comprising a pair ofpolarizing plates and a liquid crystal cell provided between them,wherein the polarizing plate comprises a pair of protective films and apolarizing membrane provided between them, and the protective film onthe screen side is a diffusing film comprising a transparent resin inwhich scatterers are dispersed, wherein the difference between therefractive index of the transparent resin and that of the scatterers isin the range of 0.04 to 1.5, and wherein scatterers are flat particleshaving particle sizes in the range of 0.1 to 50 μm.
 20. A liquid crystaldisplay of reflection type comprising a reflection board, a liquidcrystal cell and a polarizing plate in this order, wherein thepolarizing plate comprises a pair of protective films and a polarizingmembrane provided between them, and the protective film on the screenside is a diffusing film comprising a transparent resin in whichscatterers are dispersed, wherein the difference between the refractiveindex of the transparent resin and that of the scatterers is in therange of 0.04 to 1.5, and wherein scatterers are flat particles havingparticle sizes in the range of 0.1 to 50 μm.